diff --git a/s3/s3.go b/s3/s3.go
index 90754a2..9366af4 100644
--- a/s3/s3.go
+++ b/s3/s3.go
@@ -20,13 +20,15 @@ import (
 	"github.com/aws/aws-sdk-go/service/s3/s3manager"
 	"github.com/benbjohnson/litestream"
 	"github.com/benbjohnson/litestream/internal"
-	"github.com/davecgh/go-spew/spew"
 )
 
 const (
 	DefaultRetentionInterval = 1 * time.Hour
 )
 
+// MaxKeys is the number of keys S3 can operate on per batch.
+const MaxKeys = 1000
+
 var _ litestream.Replica = (*Replica)(nil)
 
 // Replica is a replica that replicates a DB to an S3 bucket.
@@ -417,8 +419,6 @@ func (r *Replica) retainer(ctx context.Context) {
 // CalcPos returns the position for the replica for the current generation.
 // Returns a zero value if there is no active generation.
 func (r *Replica) CalcPos(generation string) (pos litestream.Pos, err error) {
-	println("dbg/calcpos", generation)
-
 	if err := r.Init(context.Background()); err != nil {
 		return pos, err
 	}
@@ -429,7 +429,6 @@ func (r *Replica) CalcPos(generation string) (pos litestream.Pos, err error) {
 	if pos.Index, err = r.MaxSnapshotIndex(generation); err != nil {
 		return litestream.Pos{}, err
 	}
-	println("dbg/calcpos.snapshotindex", pos.Index)
 
 	index := -1
 	var offset int64
@@ -438,9 +437,6 @@ func (r *Replica) CalcPos(generation string) (pos litestream.Pos, err error) {
 		Prefix:    aws.String(r.WALDir(generation) + "/"),
 		Delimiter: aws.String("/"),
 	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
-		println("dbg/calcpos.page")
-		spew.Dump(page)
-
 		for _, obj := range page.Contents {
 			key := path.Base(*obj.Key)
 
@@ -548,7 +544,6 @@ func (r *Replica) Init(ctx context.Context) (err error) {
 }
 
 func (r *Replica) Sync(ctx context.Context) (err error) {
-	println("dbg/s3.sync")
 	if err := r.Init(ctx); err != nil {
 		return err
 	}
@@ -622,7 +617,6 @@ func (r *Replica) syncWAL(ctx context.Context) (err error) {
 		r.WALDir(rd.Pos().Generation),
 		litestream.FormatWALPathWithOffsetSize(rd.Pos().Index, rd.Pos().Offset, int64(len(b)))+".gz",
 	)
-	println("dbg/syncwal", walPath)
 
 	if _, err := r.uploader.Upload(&s3manager.UploadInput{
 		Bucket: aws.String(r.Bucket),
@@ -641,72 +635,90 @@ func (r *Replica) syncWAL(ctx context.Context) (err error) {
 }
 
 // SnapshotReader returns a reader for snapshot data at the given generation/index.
-// Returns os.ErrNotExist if no matching index is found.
 func (r *Replica) SnapshotReader(ctx context.Context, generation string, index int) (io.ReadCloser, error) {
-	dir := r.SnapshotDir(generation)
-	fis, err := ioutil.ReadDir(dir)
+	if err := r.Init(ctx); err != nil {
+		return nil, err
+	}
+
+	// Pipe download to return an io.Reader.
+	out, err := r.s3.GetObjectWithContext(ctx, &s3.GetObjectInput{
+		Bucket: aws.String(r.Bucket),
+		Key:    aws.String(r.SnapshotPath(generation, index)),
+	})
 	if err != nil {
 		return nil, err
 	}
 
-	for _, fi := range fis {
-		// Parse index from snapshot filename. Skip if no match.
-		idx, ext, err := litestream.ParseSnapshotPath(fi.Name())
-		if err != nil || index != idx {
-			continue
-		}
-
-		// Open & return the file handle if uncompressed.
-		f, err := os.Open(path.Join(dir, fi.Name()))
-		if err != nil {
-			return nil, err
-		} else if ext == ".snapshot" {
-			return f, nil // not compressed, return as-is.
-		}
-		// assert(ext == ".snapshot.gz", "invalid snapshot extension")
-
-		// If compressed, wrap in a gzip reader and return with wrapper to
-		// ensure that the underlying file is closed.
-		r, err := gzip.NewReader(f)
-		if err != nil {
-			f.Close()
-			return nil, err
-		}
-		return internal.NewReadCloser(r, f), nil
+	// Decompress the snapshot file.
+	gr, err := gzip.NewReader(out.Body)
+	if err != nil {
+		out.Body.Close()
+		return nil, err
 	}
-	return nil, os.ErrNotExist
+	return internal.NewReadCloser(gr, out.Body), nil
 }
 
 // WALReader returns a reader for WAL data at the given index.
 // Returns os.ErrNotExist if no matching index is found.
 func (r *Replica) WALReader(ctx context.Context, generation string, index int) (io.ReadCloser, error) {
-	panic("TODO")
-	/*
-		filename := r.WALPath(generation, index)
+	if err := r.Init(ctx); err != nil {
+		return nil, err
+	}
 
-		// Attempt to read uncompressed file first.
-		f, err := os.Open(filename)
-		if err == nil {
-			return f, nil // file exist, return
-		} else if err != nil && !os.IsNotExist(err) {
-			return nil, err
+	// Collect all files for the index.
+	var keys []string
+	var offset int64
+	var innerErr error
+	if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
+		Bucket: aws.String(r.Bucket),
+		Prefix: aws.String(path.Join(r.WALDir(generation), fmt.Sprintf("%016x_", index))),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		for _, obj := range page.Contents {
+			// Read the offset & size from the filename. We need to check this
+			// against a running offset to ensure there are no gaps.
+			_, off, sz, _, err := litestream.ParseWALPath(path.Base(*obj.Key))
+			if err != nil {
+				continue
+			} else if off != offset {
+				innerErr = fmt.Errorf("out of sequence wal segments: %s/%016x", generation, index)
+				return false
+			}
+
+			keys = append(keys, *obj.Key)
+			offset += sz
 		}
+		return true
+	}); err != nil {
+		return nil, err
+	} else if innerErr != nil {
+		return nil, innerErr
+	}
 
-		// Otherwise read the compressed file. Return error if file doesn't exist.
-		f, err = os.Open(filename + ".gz")
+	// Open each file and concatenate into a multi-reader.
+	var mrc multiReadCloser
+	for _, key := range keys {
+		// Pipe download to return an io.Reader.
+		out, err := r.s3.GetObjectWithContext(ctx, &s3.GetObjectInput{
+			Bucket: aws.String(r.Bucket),
+			Key:    aws.String(key),
+		})
 		if err != nil {
+			mrc.Close()
 			return nil, err
 		}
 
-		// If compressed, wrap in a gzip reader and return with wrapper to
-		// ensure that the underlying file is closed.
-		rd, err := gzip.NewReader(f)
+		// Decompress the snapshot file.
+		gr, err := gzip.NewReader(out.Body)
 		if err != nil {
-			f.Close()
+			out.Body.Close()
+			mrc.Close()
 			return nil, err
 		}
-		return internal.NewReadCloser(rd, f), nil
-	*/
+
+		mrc.readers = append(mrc.readers, internal.NewReadCloser(gr, out.Body))
+	}
+
+	return &mrc, nil
 }
 
 // EnforceRetention forces a new snapshot once the retention interval has passed.
@@ -752,44 +764,63 @@ func (r *Replica) EnforceRetention(ctx context.Context) (err error) {
 		// Delete generations if it has no snapshots being retained.
 		if snapshot == nil {
 			log.Printf("%s(%s): generation %q has no retained snapshots, deleting", r.db.Path(), r.Name(), generation)
-			if err := os.RemoveAll(r.GenerationDir(generation)); err != nil {
+			if err := r.deleteGenerationBefore(ctx, generation, -1); err != nil {
 				return fmt.Errorf("cannot delete generation %q dir: %w", generation, err)
 			}
 			continue
 		}
 
 		// Otherwise delete all snapshots & WAL files before a lowest retained index.
-		if err := r.deleteGenerationSnapshotsBefore(ctx, generation, snapshot.Index); err != nil {
-			return fmt.Errorf("cannot delete generation %q snapshots before index %d: %w", generation, snapshot.Index, err)
-		} else if err := r.deleteGenerationWALBefore(ctx, generation, snapshot.Index); err != nil {
-			return fmt.Errorf("cannot delete generation %q wal before index %d: %w", generation, snapshot.Index, err)
+		if err := r.deleteGenerationBefore(ctx, generation, snapshot.Index); err != nil {
+			return fmt.Errorf("cannot delete generation %q files before index %d: %w", generation, snapshot.Index, err)
 		}
 	}
 
 	return nil
 }
 
-// deleteGenerationSnapshotsBefore deletes snapshot before a given index.
-func (r *Replica) deleteGenerationSnapshotsBefore(ctx context.Context, generation string, index int) (err error) {
-	dir := r.SnapshotDir(generation)
+func (r *Replica) deleteGenerationBefore(ctx context.Context, generation string, index int) (err error) {
+	// Collect all files for the generation.
+	var objIDs []*s3.ObjectIdentifier
+	if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
+		Bucket: aws.String(r.Bucket),
+		Prefix: aws.String(r.GenerationDir(generation)),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		for _, obj := range page.Contents {
+			// Skip snapshots or WALs that are after the search index unless -1.
+			if index != -1 {
+				if idx, _, err := litestream.ParseSnapshotPath(path.Base(*obj.Key)); err == nil && idx >= index {
+					continue
+				} else if idx, _, _, _, err := litestream.ParseWALPath(path.Base(*obj.Key)); err == nil && idx >= index {
+					continue
+				}
+			}
 
-	fis, err := ioutil.ReadDir(dir)
-	if os.IsNotExist(err) {
-		return nil
-	} else if err != nil {
+			objIDs = append(objIDs, &s3.ObjectIdentifier{Key: obj.Key})
+		}
+		return true
+	}); err != nil {
 		return err
 	}
 
-	for _, fi := range fis {
-		idx, _, err := litestream.ParseSnapshotPath(fi.Name())
-		if err != nil {
-			continue
-		} else if idx >= index {
-			continue
+	// Delete all files in batches.
+	for i := 0; i < len(objIDs); i += MaxKeys {
+		j := i + MaxKeys
+		if j > len(objIDs) {
+			j = len(objIDs)
 		}
 
-		log.Printf("%s(%s): generation %q snapshot no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
-		if err := os.Remove(path.Join(dir, fi.Name())); err != nil {
+		for _, objID := range objIDs[i:j] {
+			log.Printf("%s(%s): generation %q file no longer retained, deleting %s", r.db.Path(), r.Name(), generation, path.Base(*objID.Key))
+		}
+
+		if _, err := r.s3.DeleteObjectsWithContext(ctx, &s3.DeleteObjectsInput{
+			Bucket: aws.String(r.Bucket),
+			Delete: &s3.Delete{
+				Objects: objIDs[i:j],
+				Quiet:   aws.Bool(true),
+			},
+		}); err != nil {
 			return err
 		}
 	}
@@ -797,30 +828,36 @@ func (r *Replica) deleteGenerationSnapshotsBefore(ctx context.Context, generatio
 	return nil
 }
 
-// deleteGenerationWALBefore deletes WAL files before a given index.
-func (r *Replica) deleteGenerationWALBefore(ctx context.Context, generation string, index int) (err error) {
-	dir := r.WALDir(generation)
-
-	fis, err := ioutil.ReadDir(dir)
-	if os.IsNotExist(err) {
-		return nil
-	} else if err != nil {
-		return err
-	}
-
-	for _, fi := range fis {
-		idx, _, _, _, err := litestream.ParseWALPath(fi.Name())
-		if err != nil {
-			continue
-		} else if idx >= index {
-			continue
-		}
-
-		log.Printf("%s(%s): generation %q wal no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
-		if err := os.Remove(path.Join(dir, fi.Name())); err != nil {
-			return err
-		}
-	}
-
-	return nil
+type multiReadCloser struct {
+	readers []io.ReadCloser
+}
+
+func (mr *multiReadCloser) Read(p []byte) (n int, err error) {
+	for len(mr.readers) > 0 {
+		n, err = mr.readers[0].Read(p)
+		if err == io.EOF {
+			if e := mr.readers[0].Close(); e != nil {
+				return n, e
+			}
+			mr.readers[0] = nil
+			mr.readers = mr.readers[1:]
+		}
+
+		if n > 0 || err != io.EOF {
+			if err == io.EOF && len(mr.readers) > 0 {
+				err = nil
+			}
+			return
+		}
+	}
+	return 0, io.EOF
+}
+
+func (mr *multiReadCloser) Close() (err error) {
+	for _, r := range mr.readers {
+		if e := r.Close(); e != nil && err == nil {
+			err = e
+		}
+	}
+	return err
 }