diff --git a/zipline/pipeline/loaders/blaze/core.py b/zipline/pipeline/loaders/blaze/core.py
index edef7c40..6f575b91 100644
--- a/zipline/pipeline/loaders/blaze/core.py
+++ b/zipline/pipeline/loaders/blaze/core.py
@@ -159,11 +159,11 @@ from six import with_metaclass, PY2, itervalues, iteritems
 from toolz import (
     complement,
     compose,
-    concat,
     flip,
     groupby,
     identity,
     memoize,
+    merge,
 )
 import toolz.curried.operator as op
 
@@ -188,6 +188,7 @@ from zipline.utils.input_validation import (
 )
 from zipline.utils.numpy_utils import bool_dtype, categorical_dtype
 from zipline.utils.pandas_utils import sort_values
+from zipline.utils.pool import SequentialPool
 from zipline.utils.preprocess import preprocess
 
 
@@ -915,19 +916,40 @@ class BlazeLoader(dict):
         object.
     data_query_time : time, optional
         The time to use for the data query cutoff.
-    data_query_tz : tzinfo or str
+    data_query_tz : tzinfo or str, optional
         The timezeone to use for the data query cutoff.
+    pool : Pool, optional
+        The pool to use to run blaze queries concurrently. This object must
+        support ``imap_unordered``, ``apply`` and ``apply_async`` methods.
+
+    Attributes
+    ----------
+    pool : Pool
+        The pool to use to run blaze queries concurrently. This object must
+        support ``imap_unordered``, ``apply`` and ``apply_async`` methods.
+        It is possible to change the pool after the loader has been
+        constructed. This allows us to set a new pool for the ``global_loader``
+        like: ``global_loader.pool = multiprocessing.Pool(4)``.
+
+    See Also
+    --------
+    :class:`zipline.utils.pool.SequentialPool`
+    :class:`multiprocessing.Pool`
     """
     @preprocess(data_query_tz=optionally(ensure_timezone))
     def __init__(self,
                  dsmap=None,
                  data_query_time=None,
-                 data_query_tz=None):
+                 data_query_tz=None,
+                 pool=SequentialPool()):
         self.update(dsmap or {})
         check_data_query_args(data_query_time, data_query_tz)
         self._data_query_time = data_query_time
         self._data_query_tz = data_query_tz
 
+        # explicitly public
+        self.pool = pool
+
     @classmethod
     @memoize(cache=WeakKeyDictionary())
     def global_instance(cls):
@@ -948,11 +970,11 @@ class BlazeLoader(dict):
         )
 
     def load_adjusted_array(self, columns, dates, assets, mask):
-        return dict(
-            concat(map(
+        return merge(
+            self.pool.imap_unordered(
                 partial(self._load_dataset, dates, assets, mask),
-                itervalues(groupby(getdataset, columns))
-            ))
+                itervalues(groupby(getdataset, columns)),
+            ),
         )
 
     def _load_dataset(self, dates, assets, mask, columns):
@@ -1022,21 +1044,22 @@ class BlazeLoader(dict):
             materialized_checkpoints = pd.DataFrame(columns=colnames)
             lower = None
 
-        materialized_expr = collect_expr(expr, lower)
+        materialized_expr = self.pool.apply_async(collect_expr, (expr, lower))
+        materialized_deltas = (
+            self.pool.apply(collect_expr, (deltas, lower))
+            if deltas is not None else
+            pd.DataFrame(columns=colnames)
+        )
+
         if materialized_checkpoints is not None:
             materialized_expr = pd.concat(
                 (
                     materialized_checkpoints,
-                    materialized_expr,
+                    materialized_expr.get(),
                 ),
                 ignore_index=True,
                 copy=False,
             )
-        materialized_deltas = (
-            collect_expr(deltas, lower)
-            if deltas is not None else
-            pd.DataFrame(columns=colnames)
-        )
 
         # It's not guaranteed that assets returned by the engine will contain
         # all sids from the deltas table; filter out such mismatches here.
@@ -1147,23 +1170,24 @@ class BlazeLoader(dict):
                 shape=(len(mask), 1), fill_value=True, dtype=bool_dtype,
             )
 
-        for column_idx, column in enumerate(columns):
-            column_name = column.name
-            yield column, AdjustedArray(
+        return {
+            column: AdjustedArray(
                 column_view(
-                    dense_output[column_name].values.astype(column.dtype),
+                    dense_output[column.name].values.astype(column.dtype),
                 ),
                 mask,
                 adjustments_from_deltas(
                     dates,
                     sparse_output[TS_FIELD_NAME].values,
                     column_idx,
-                    column_name,
+                    column.name,
                     asset_idx,
                     sparse_deltas,
                 ),
                 column.missing_value,
             )
+            for column_idx, column in enumerate(columns)
+        }
 
 global_loader = BlazeLoader.global_instance()
 
diff --git a/zipline/utils/functional.py b/zipline/utils/functional.py
index a5282bff..791be004 100644
--- a/zipline/utils/functional.py
+++ b/zipline/utils/functional.py
@@ -330,3 +330,19 @@ def set_attribute(name, value):
 # Example:
 with_name = set_attribute('__name__')
 with_doc = set_attribute('__doc__')
+
+
+def let(a):
+    """Box a value to be bound in a for binding.
+
+    Examples
+    --------
+    .. code-block:: python
+
+       [f(y, y) for x in xs for y in let(g(x)) if p(y)]
+
+    Here, ``y`` is available in both the predicate and the expression
+    of the comprehension. We can see that this allows us to cache the work
+    of computing ``g(x)`` even within the expression.
+    """
+    return a,
diff --git a/zipline/utils/pool.py b/zipline/utils/pool.py
new file mode 100644
index 00000000..c39a3df9
--- /dev/null
+++ b/zipline/utils/pool.py
@@ -0,0 +1,136 @@
+from six.moves import map as imap
+from toolz import compose, identity
+
+
+class ApplyAsyncResult(object):
+    """An object that boxes results for calls to
+    :meth:`~zipline.utils.pool.SequentialPool.apply_async`.
+
+    Parameters
+    ----------
+    value : any
+        The result of calling the function, or any exception that was raised.
+    successful : bool
+        If ``True``, ``value`` is the return value of the function.
+        If ``False``, ``value`` is the exception that was raised when calling
+        the functions.
+    """
+    def __init__(self, value, successful):
+        self._value = value
+        self._successful = successful
+
+    def successful(self):
+        """Did the function execute without raising an exception?
+        """
+        return self._successful
+
+    def get(self):
+        """Return the result of calling the function or reraise any exceptions
+        that were raised.
+        """
+        if not self._successful:
+            raise self._value
+        return self._value
+
+    def ready(self):
+        """Has the function finished executing.
+
+        Notes
+        -----
+        In the :class:`~zipline.utils.pool.SequentialPool` case, this is always
+        ``True``.
+        """
+        return True
+
+    def wait(self):
+        """Wait until the function is finished executing.
+
+        Notes
+        -----
+        In the :class:`~zipline.utils.pool.SequentialPool` case, this is a nop
+        because the function is computed eagerly in the same thread as the
+        call to :meth:`~zipline.utils.pool.SequentialPool.apply_async`.
+        """
+        pass
+
+
+class SequentialPool(object):
+    """A dummy pool object that iterates sequentially in a single thread.
+
+    Methods
+    -------
+    map(f: callable[A, B], iterable: iterable[A]) -> list[B]
+        Apply a function to each of the elements of ``iterable``.
+    imap(f: callable[A, B], iterable: iterable[A]) -> iterable[B]
+        Lazily apply a function to each of the elements of ``iterable``.
+    imap_unordered(f: callable[A, B], iterable: iterable[A]) -> iterable[B]
+        Lazily apply a function to each of the elements of ``iterable`` but
+        yield values as they become available. The resulting iterable is
+        unordered.
+
+    Notes
+    -----
+    This object is useful for testing to mock out the ``Pool`` interface
+    provided by gevent or multiprocessing.
+
+    See Also
+    --------
+    :class:`multiprocessing.Pool`
+    """
+    map = staticmethod(compose(list, imap))
+    imap = imap_unordered = staticmethod(imap)
+
+    @staticmethod
+    def apply_async(f, args=(), kwargs=None, callback=None):
+        """Apply a function but emulate the API of an asynchronous call.
+
+        Parameters
+        ----------
+        f : callable
+            The function to call.
+        args : tuple, optional
+            The positional arguments.
+        kwargs : dict, optional
+            The keyword arguments.
+
+        Returns
+        -------
+        future : ApplyAsyncResult
+            The result of calling the function boxed in a future-like api.
+
+        Notes
+        -----
+        This calls the function eagerly but wraps it so that ``SequentialPool``
+        can be used where a :class:`multiprocessing.Pool` or
+        :class:`gevent.pool.Pool` would be used.
+        """
+        try:
+            value = (identity if callback is None else callback)(
+                f(*args, **kwargs or {}),
+            )
+            successful = True
+        except Exception as e:
+            value = e
+            successful = False
+
+        return ApplyAsyncResult(value, successful)
+
+    @staticmethod
+    def apply(f, args=(), kwargs=None):
+        """Apply a function.
+
+        Parameters
+        ----------
+        f : callable
+            The function to call.
+        args : tuple, optional
+            The positional arguments.
+        kwargs : dict, optional
+            The keyword arguments.
+
+        Returns
+        -------
+        result : any
+            f(*args, **kwargs)
+        """
+        return f(*args, **kwargs or {})