diff --git a/zipline/finance/trading.py b/zipline/finance/trading.py
index dd6345d4..53ac8f2f 100644
--- a/zipline/finance/trading.py
+++ b/zipline/finance/trading.py
@@ -11,8 +11,8 @@ log = logbook.Logger('Transaction Simulator')
 class TransactionSimulator(object):
     UPDATER = True
 
-    def __init__(self, open_orders, style=SIMULATION_STYLE.PARTIAL_VOLUME):
-        self.open_orders                = open_orders
+    def __init__(self, sid_filter, style=SIMULATION_STYLE.PARTIAL_VOLUME):
+        self.open_orders                = {}
         self.txn_count                  = 0
         self.trade_window               = datetime.timedelta(seconds=30)
         self.orderTTL                   = datetime.timedelta(days=1)
@@ -27,6 +27,12 @@ class TransactionSimulator(object):
         elif style == SIMULATION_STYLE.NOOP:
             self.apply_trade_to_open_orders = self.simulate_noop
 
+        for sid in sid_filter:
+            self.open_orders[sid] = []
+
+    def place_order(self, order):
+        self.open_orders[order.sid].append(order)
+
     def update(self, event):
         event.TRANSACTION = None
         if event.type == zp.DATASOURCE_TYPE.TRADE:
diff --git a/zipline/gens/composites.py b/zipline/gens/composites.py
index f7875816..2b9905b7 100644
--- a/zipline/gens/composites.py
+++ b/zipline/gens/composites.py
@@ -15,7 +15,7 @@ def date_sorted_sources(*sources):
     """
     Takes an iterable of SortBundles, generating namestrings and initialized datasources
     for each before piping them into a date_sort.
-n    """
+    """
 
     for source in sources:
         assert iter(source), "Source %s not iterable" % source
@@ -55,7 +55,7 @@ def merged_transforms(sorted_stream, bundles):
     tnfms_with_streams = zip(split, bundles)
 
     # Convert the copies into transform streams.
-    tnfms = [
+    tnfm_gens = [
         StatefulTransform(
             stream_copy, 
             bundle.tnfm, 
@@ -64,8 +64,6 @@ def merged_transforms(sorted_stream, bundles):
         )
         for stream_copy, bundle in tnfms_with_streams
     ]
-    tnfm_gens = [tnfm.gen() for tnfm in tnfms]
-
 
     # Roundrobin the outputs of our transforms to create a single flat stream.
     to_merge = roundrobin(tnfm_gens, namestrings)
diff --git a/zipline/gens/examples.py b/zipline/gens/examples.py
index 3027eab7..38964f01 100644
--- a/zipline/gens/examples.py
+++ b/zipline/gens/examples.py
@@ -11,7 +11,7 @@ from zipline.gens.composites import SourceBundle, TransformBundle, \
     date_sorted_sources, merged_transforms
 from zipline.gens.tradegens import SpecificEquityTrades
 from zipline.gens.transform import MovingAverage, Passthrough, StatefulTransform
-from zipline.gens.tradesimulation import trade_simulation_client as tsc
+from zipline.gens.tradesimulation import TradeSimulationClient as tsc
 
 import zipline.protocol as zp
 
@@ -21,6 +21,7 @@ if __name__ == "__main__":
     #Set up source a. One minute between events.
     args_a = tuple()
     kwargs_a = {
+        'count'  : 2000,
         'sids'   : [1,2,3],
         'start'  : datetime(2012,1,3,15, tzinfo = pytz.utc),
         'delta'  : timedelta(minutes = 10),
@@ -31,6 +32,7 @@ if __name__ == "__main__":
     #Set up source b. Two minutes between events.
     args_b = tuple()
     kwargs_b = {
+        'count'  : 2000,
         'sids'   : [2,3,4],
         'start'  : datetime(2012,1,3,14, tzinfo = pytz.utc),
         'delta'  : timedelta(minutes = 10),
diff --git a/zipline/gens/tradegens.py b/zipline/gens/tradegens.py
index a8a691b5..b1a0ed96 100644
--- a/zipline/gens/tradegens.py
+++ b/zipline/gens/tradegens.py
@@ -84,7 +84,7 @@ class SpecificEquityTrades(object):
         self.generator = self.create_fresh_generator()
 
     def __iter__(self):
-        return self.generator
+        return self
 
     def next(self):
         return self.generator.next()
diff --git a/zipline/gens/tradesimulation.py b/zipline/gens/tradesimulation.py
index a4a576fe..5e8db374 100644
--- a/zipline/gens/tradesimulation.py
+++ b/zipline/gens/tradesimulation.py
@@ -9,7 +9,7 @@ from zipline.gens.transform import StatefulTransform
 from zipline.finance.trading import TransactionSimulator
 from zipline.finance.performance import PerformanceTracker
 
-def trade_simulation_client(stream_in, algo, environment, sim_style):
+class TradeSimulationClient(object):
     """
     Generator that takes the expected output of a merge, a user
     algorithm, a trading environment, and a simulator style as
@@ -42,61 +42,123 @@ def trade_simulation_client(stream_in, algo, environment, sim_style):
     overwritten so that only the most recent snapshot of the universe
     is sent to the algo.
     """
-
-    #============
-    # Algo Setup
-    #============
-
-    # Initialize txn_sim's dictionary of orders here so that we can
-    # reference it from within the user's algorithm.
     
-    sids = algo.get_sid_filter()
-    open_orders = {}
+    def __init__(self, stream_in, algo, environment, sim_style):
 
-    for sid in sids:
-        open_orders[sid] = []
+        self.stream_in = stream_in
+        self.algo = algo
+        self.sids = algo.get_sid_filter()
+        self.environment = environment
+        self.style = sim_style
+
+        self.__generator = None
+        
+
+    def get_hash(self):
+        """
+        There should only ever be one TSC in the system.
+        """
+        return self.__class__.__name__ + hash_args()
+
+    def __iter__(self):
+        return self
+
+    def next(self):
+        if self.__generator:
+            return self.__generator.next()
+        else:
+            self.__generator = self.run_simulation()
+            return self.__generator.next()
+            
+    def run_simulation(self):
+        """
+        Main generator work loop.
+        """
+        # Simulate filling any open orders made by the previous run of
+        # the user's algorithm.  Sets the txn field to true on any
+        # event that results in a filled order.
+        ordering_client = StatefulTransform(
+            self.stream_in,
+            TransactionSimulator,
+            self.sids,
+            style = self.style
+        )
+        # Pipe the events with transactions to perf. This will remove
+        # the txn field added by TransactionSimulator and replace it
+        # with a portfolio object to be passed to the user's
+        # algorithm. Also adds a PERF_MESSAGE field which is usually
+        # none, but contains an update message once per day.
+        current_portfolio = StatefulTransform(
+            ordering_client,
+            PerformanceTracker,
+            self.environment,
+            self.sids
+        )
+        # Pass both the ordering client's state and messages with the
+        # current portfolio into the algorithm for simulation.
+        algo_results = AlgorithmSimulator(
+            current_portfolio,
+            ordering_client.state,
+            self.algo, 
+        )
+        
+        for message in algo_results:        
+            yield message
+
+
+class AlgorithmSimulator(object):
     
-    # Pipe the in stream into the transaction simulator.
-    # Creates a txn field on the event containing transaction
-    # information if we filled any pending orders on the event's sid.
-    # TRANSACTION is None if we didn't fill any orders.
-    with_txns = StatefulTransform(
-        stream_in,
-        TransactionSimulator,
-        open_orders,
-        style = sim_style
-    )
-
-    # Pipe the events with transactions to perf. This will remove the
-    # txn field added by TransactionSimulator and replace it with
-    # a portfolio object to be passed to the user's algorithm. Also adds
-    # a PERF_MESSAGE field which is usually none, but contains an update
-    # message once per day.
-    with_portfolio_and_perf_msg = StatefulTransform(
-        with_txns,
-        PerformanceTracker,
-        environment,
-        sids
-    )
-
-    # Batch the event stream by dt to be processed by the user's algo.
-    # Yields perf messages whenever it encounters them.
-    perf_messages = algo_simulator(with_portfolio_and_perf_msg, sids, algo, open_orders)
-
-    for message in perf_messages:        
-        yield message
-
-
-def algo_simulator(stream_in, sids, algo, order_book):
+    def __init__(self, stream_in, order_book, algo): 
     
-    simulation_dt = None
+        self.stream_in = stream_in
 
-    # Closure to pass into the user's algo to allow placing orders
-    # into the txn_sim's dict of open orders.
-    def order(sid, amount):
-        assert sid in sids, "Order on invalid sid: %i" % sid
+        # We extract the order book from the txn client so that 
+        # the algo can place new orders.
+        self.order_book = order_book
+
+        self.algo = algo
+        self.sids = algo.get_sid_filter()
+
+        # Monkey patch the user algorithm to place orders in the
+        # txn_sim order book.
+        self.algo.set_order(self.order)
+        self.algo.set_logger(logbook.Logger("Algolog"))
+
+        # Call the user's initialize method.
+        self.algo.initialize()
+
+        # The algorithm's universe as of our most recent event.
+        self.universe = ndict()
+        
+        for sid in self.sids:
+            self.universe[sid] = ndict()
+        self.universe.portfolio = None
+
+        # We don't have a datetime for the current snapshot until we
+        # receive a message.
+        self.simulation_dt = None
+        self.this_snapshot_dt = None
+
+        self.__generator = None
+
+    def __iter__(self):
+        return self
+    
+    def next(self):
+        if self.__generator:
+            return self.__generator.next()
+        else:
+            self.__generator = self._gen()
+            return self.__generator.next()
+
+    def order(self, sid, amount):
+        """
+        Closure to pass into the user's algo to allow placing orders
+        into the txn_sim's dict of open orders.
+        """
+        assert sid in self.sids, "Order on invalid sid: %i" % sid
         order = ndict({
-            'dt'     : simulation_dt,
+            'dt'     : self.simulation_dt,
             'sid'    : sid,
             'amount' : int(amount),
             'filled' : 0
@@ -104,91 +166,105 @@ def algo_simulator(stream_in, sids, algo, order_book):
 
         # Tell the user if they try to buy 0 shares of something.
         if order.amount == 0:
-            log = "requested to trade zero shares of {sid}".format(
+            zero_message = "Requested to trade zero shares of {sid}".format(
                 sid=event.sid
             )
-            log.debug(log)
+            log.debug(zero_message)
+            # Don't bother placing orders for 0 shares.
             return 
-        
-        order_book[sid].append(order)
-    
-    # Set the algo's order method.
-    algo.set_order(order)
 
-    # Provide a logbook logging interface to user code.
-    algo.set_logger(logbook.Logger("Algolog"))
+        # Add non-zero orders to the order book.  
+        # !!!IMPORTANT SIDE-EFFECT!!!
+        # This modifies the internal state of the transaction
+        # simulator so that it can fill the placed order when it
+        # receives its next message.
+        self.order_book.place_order(order)
 
-    # Call user-defined initialize method before we process any
-    # events.
-    algo.initialize()
-    
-    universe = ndict()
-    for sid in sids:
-        universe[sid] = ndict()
-    universe.portfolio = None
-    this_snapshot_dt = None
-
-    for event in stream_in:
-        # Yield any perf messages received to be relayed back to the browser.
-        if event.perf_message:
-            yield event.perf_message
-            del event['perf_message']
-
-        # This should only happen for the first event we run.
-        if simulation_dt == None:
-            simulation_dt = event.dt
-            
-        # If we are currently creating a new message and this update
-        # matches the message dt, update the state of the universe.
-
-        if this_snapshot_dt != None:
-
-            if event.dt == this_snapshot_dt:
-                update_universe(event, universe)
-
-            # If we are constructing a snapshot and we hit a new dt, call
-            # handle_data and record how long it takes.
-            else:
-                start_tic = datetime.now()
-                algo.handle_data(universe)
-                stop_tic = datetime.now()
-
-                # How long did you take?
-                delta = stop_tic - start_tic
-
-                # Update the simulation time.
-                simulation_dt = this_snapshot_dt + delta
+    def _gen(self):
+        """
+        Internal generator work loop.
+        """
+        for event in self.stream_in:
+            # Yield any perf messages received to be relayed back to the browser.
+            if event.perf_message:
+                yield event.perf_message
+                del event['perf_message']
                 
-                # Update the universe with the new event.
-                update_universe(event, universe)
+            # This should only happen for the first event we run.
+            if self.simulation_dt == None:
+                self.simulation_dt = event.dt
+            
+            # ======================
+            # Time Compression Logic
+            # ======================
+        
+            if self.this_snapshot_dt != None:
+                self.update_current_snapshot(event)
 
-                # If the current event is later than the simulation
-                # time, update the universe and start constructing
-                # another snapshot.
-                if event.dt >= simulation_dt:
-                    this_snapshot_dt = event.dt
-                else:
-                    this_snapshot_dt = None
-        # We have been fastforwarding.  Update the universe
-        # and check if we can start a new snapshot.
+            # The algorithm has been missing events because it took
+            # too long processing.  Update the universe with data from
+            # this event, then check if enough time has passed that we
+            # can start a new snapshot.
+            else: 
+                self.update_universe(event)
+                if event.dt >= self.simulation_dt:
+                    self.this_snapshot_dt = event.dt
+
+    def update_current_snapshot(self, event):
+        """
+        Update our current snapshot of the universe. Call handle_data if 
+        """
+        # The new event matches our snapshot dt. Just update the
+        # universe and move on.
+        if event.dt == self.this_snapshot_dt:
+            self.update_universe(event)
+            
+        # The new event does not match our snapshot.  
         else:
-            update_universe(event, universe)
-            if event.dt >= simulation_dt:
-                this_snapshot_dt = event.dt
-
+            self.simulate_current_snapshot()
+            
+            # Once we've finished simulating the old snapshot,
+            # we can update the universe with the new event.
+            self.update_universe(event)
+            
+            # The current event is later than the simulation time,
+            # which means the algorithm finished quickly enough to
+            # receive the new event.  Start a new snapshot with this
+            # event's dt.
+            if event.dt >= self.simulation_dt:
+                self.this_snapshot_dt = event.dt
                 
-
+            # The algorithm spent enough time processing that it
+            # missed the new event. Wait to start a new snapshot until
+            # the events catch up to the algo's simulated dt.
+            else:
+                self.this_snapshot_dt = None
+                
+    def simulate_current_snapshot(self):
+        """
+        Run the user's algo against our current snapshot and update the algo's
+        simulated time.
+        """        
+        start_tic = datetime.now()
+        self.algo.handle_data(self.universe)
+        stop_tic = datetime.now()
+            
+        # How long did you take?
+        delta = stop_tic - start_tic
+            
+        # Update the simulation time.
+        self.simulation_dt = self.this_snapshot_dt + delta
         
-def update_universe(event, universe):
-
-    universe.portfolio = event.portfolio
-    del event['portfolio']
+    def update_universe(self, event):
+        """
+        Update the universe with new event information.
+        """
+        # Update our portfolio.
+        self.universe.portfolio = event.portfolio
     
-    event_sid = event.sid
-    del event['sid']
-        
-    for field in event.keys():
-        universe[event_sid][field] = event[field]
+        # Update our knowledge of this event's sid
+        for field in event.keys():
+            self.universe[event.sid][field] = event[field]
             
     
     
diff --git a/zipline/gens/transform.py b/zipline/gens/transform.py
index 4d453927..f230f99d 100644
--- a/zipline/gens/transform.py
+++ b/zipline/gens/transform.py
@@ -42,7 +42,7 @@ def functional_transform(stream_in, func, *args, **kwargs):
 class StatefulTransform(object):
     """
     Generic transform generator that takes each message from an
-    in-stream and passes it to a state class.  For each call to
+    in-stream and passes it to a state object.  For each call to
     update, the state class must produce a message to be fed
     downstream. Any transform class with the FORWARDER class variable
     set to true will forward all fields in the original message.
@@ -63,16 +63,26 @@ class StatefulTransform(object):
         # Create an instance of our transform class.
         self.state = tnfm_class(*args, **kwargs)
         
-        # Generate the string associated with this generator's output.
+        # Create the string associated with this generator's output.
         self.namestring = tnfm_class.__name__ + hash_args(*args, **kwargs)
+
+        # Generator isn't initialized until someone calls __iter__ or next().
+        self.__generator = None
         
     def get_hash(self):
         return self.namestring
 
+    def next(self):
+        if self.__generator:
+            return self.__generator.next()
+        else:
+            self.__generator = self._gen()
+            return self.__generator.next()
+
     def __iter__(self):
-        return self.gen()
-        
-    def gen(self):
+        return self
+                
+    def _gen(self):
         # IMPORTANT: Messages may contain pointers that are shared with
         # other streams, so we only manipulate copies.
         for message in self.stream_in: