diff --git a/odc/loader/_builder.py b/odc/loader/_builder.py
index 7f431f3..8b4d999 100644
--- a/odc/loader/_builder.py
+++ b/odc/loader/_builder.py
@@ -33,9 +33,15 @@
 from odc.geo.geobox import GeoBox, GeoBoxBase, GeoboxTiles
 from odc.geo.xr import xr_coords
 
-from ._reader import nodata_mask, resolve_dst_fill_value, resolve_src_nodata
+from ._reader import (
+    ReaderDaskAdaptor,
+    nodata_mask,
+    resolve_dst_fill_value,
+    resolve_src_nodata,
+)
 from ._utils import SizedIterable, pmap
 from .types import (
+    DaskRasterReader,
     MultiBandRasterSource,
     RasterGroupMetadata,
     RasterLoadParams,
@@ -154,6 +160,7 @@ def __init__(
         env: Dict[str, Any],
         rdr: ReaderDriver,
         chunks: Mapping[str, int],
+        mode: Literal["auto"] | Literal["mem"] | Literal["concurrency"] = "auto",
     ) -> None:
         gbox = gbt.base
         assert isinstance(gbox, GeoBox)
@@ -161,6 +168,8 @@ def __init__(
         chunk_tyx = (chunks.get("time", 1), *gbt.chunk_shape((0, 0)).yx)
         chunks = {**chunks}
         chunks.update(dict(zip(["time", "y", "x"], chunk_tyx)))
+        if mode == "auto":
+            mode = "mem"  # current default
 
         self.cfg = cfg
         self.template = template
@@ -169,8 +178,9 @@ def __init__(
         self.gbt = gbt
         self.env = env
         self.rdr = rdr
-        self._tk = tokenize(srcs, cfg, gbt, tyx_bins, env, chunks)
+        self._tk = tokenize(srcs, cfg, gbt, tyx_bins, env, chunks, mode)
         self._chunks = chunks
+        self._mode = mode
         self._load_state = rdr.new_load(gbox, chunks=chunks)
 
     def _band_chunks(
@@ -191,7 +201,7 @@ def build(
         gbox: GeoBox,
         time: Sequence[datetime],
         bands: Mapping[str, RasterLoadParams],
-    ):
+    ) -> xr.Dataset:
         return mk_dataset(
             gbox,
             time,
@@ -200,13 +210,17 @@ def build(
             template=self.template,
         )
 
-    def _prep_sources(
-        self, name: str, dsk: dict[Key, Any], deps: list[Any]
-    ) -> tuple[str, Any]:
+    def _norm_load_state(self, deps: list[Any]) -> Any:
         load_state = self._load_state
         if is_dask_collection(load_state):
             deps.append(load_state)
             load_state = load_state.key
+        return load_state
+
+    def _prep_sources(
+        self, name: str, dsk: dict[Key, Any], deps: list[Any]
+    ) -> tuple[str, Any]:
+        load_state = self._norm_load_state(deps)
 
         tk = self._tk
         src_key = f"open-{name}-{tk}"
@@ -223,6 +237,35 @@ def _prep_sources(
                 )
         return src_key, load_state
 
+    def _dask_rdr(self) -> DaskRasterReader:
+        if (dask_reader := self.rdr.dask_reader) is not None:
+            return dask_reader
+        return ReaderDaskAdaptor(self.rdr, self.env)
+
+    def _task_futures(
+        self,
+        task: LoadChunkTask,
+        dask_reader: DaskRasterReader,
+        deps: list[Any],
+    ) -> list[list[Any]]:
+        srcs = task.resolve_sources(self.srcs)
+        out: list[list[Any]] = []
+        ctx = self._load_state
+        cfg = task.cfg
+        dst_gbox = task.dst_gbox
+
+        for layer in srcs:
+            read_futures: list[Any] = []
+            for src in layer:
+                rdr = dask_reader.open(src, ctx)
+                fut = rdr.read(cfg, dst_gbox, selection=task.selection)
+                read_futures.append(fut)
+                deps.append(fut)
+
+            out.append(read_futures)
+
+        return out
+
     def __call__(
         self,
         shape: Tuple[int, ...],
@@ -238,6 +281,8 @@ def __call__(
         assert dtype == cfg.dtype
         assert ydim == cfg.ydim + 1  # +1 for time dimension
 
+        chunks = self._band_chunks(name, shape, ydim)
+
         tk = self._tk
         deps: list[Any] = []
         cfg_dask_key = f"cfg-{tokenize(cfg)}"
@@ -247,25 +292,48 @@ def __call__(
             cfg_dask_key: cfg,
             gbt_dask_key: self.gbt,
         }
-        src_key, load_state = self._prep_sources(name, dsk, deps)
+        dask_reader: DaskRasterReader | None = None
+        if self._mode == "mem":
+            src_key, load_state = self._prep_sources(name, dsk, deps)
+        else:
+            dask_reader = self._dask_rdr()
+            src_key, load_state = "", self._load_state
+
+        fill_value = resolve_dst_fill_value(
+            np.dtype(dtype),
+            cfg,
+            resolve_src_nodata(cfg.fill_value, cfg),
+        )
 
         band_key = f"{name}-{tk}"
-        chunks = self._band_chunks(name, shape, ydim)
 
         for task in self.load_tasks(name, shape[0]):
-            dsk[(band_key, *task.idx)] = (
-                _dask_loader_tyx,
-                task.resolve_sources_dask(src_key, dsk),
-                gbt_dask_key,
-                quote(task.idx_tyx[1:]),
-                quote(task.prefix_dims),
-                quote(task.postfix_dims),
-                cfg_dask_key,
-                self.rdr,
-                self.env,
-                load_state,
-                task.selection,
-            )
+            task_key: Key = (band_key, *task.idx)
+            if dask_reader is None:
+                dsk[task_key] = (
+                    _dask_loader_tyx,
+                    task.resolve_sources_dask(src_key, dsk),
+                    gbt_dask_key,
+                    quote(task.idx_tyx[1:]),
+                    quote(task.prefix_dims),
+                    quote(task.postfix_dims),
+                    cfg_dask_key,
+                    self.rdr,
+                    self.env,
+                    load_state,
+                    task.selection,
+                )
+            else:
+                srcs_futures = self._task_futures(task, dask_reader, deps)
+
+                dsk[task_key] = (
+                    _dask_fuser,
+                    srcs_futures,
+                    task.shape,
+                    dtype,
+                    fill_value,
+                    ydim - 1,
+                )
 
         dsk = HighLevelGraph.from_collections(band_key, dsk, dependencies=deps)
 
@@ -320,6 +388,30 @@ def _dask_loader_tyx(
         return chunk
 
 
+def _dask_fuser(
+    srcs: list[list[Any]],
+    shape: tuple[int, ...],
+    dtype: DTypeLike,
+    fill_value: float | int,
+    src_ydim: int = 0,
+):
+    assert shape[0] == len(srcs)
+    assert len(shape) >= 3  # time, ..., y, x, ...
+
+    dst = np.full(shape, fill_value, dtype=dtype)
+
+    for ti, layer in enumerate(srcs):
+        fuse_nd_slices(
+            layer,
+            fill_value,
+            dst[ti],
+            ydim=src_ydim,
+            prefilled=True,
+        )
+
+    return dst
+
+
 def fuse_nd_slices(
     srcs: Iterable[tuple[tuple[slice, slice], np.ndarray]],
     fill_value: float | int,