diff --git a/CHANGELOG.md b/CHANGELOG.md
index e72902ffd09..fa7e11df703 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -61,6 +61,8 @@
 * [ENHANCEMENT] Blocksconvert – Builder: retry block upload before giving up. #3245
 * [ENHANCEMENT] Hash ring: added instance registered timestamp to the ring. #3248
 * [ENHANCEMENT] Reduce tail latency by smoothing out spikes in rate of chunk flush operations. #3191
+* [ENHANCEMENT] Experimental Ruler API: Fetch rule groups from object storage in parallel. #3218
+* [ENHANCEMENT] Chunks GCS object storage client uses the `fields` selector to limit the payload size when listing objects in the bucket. #3218
 * [BUGFIX] No-longer-needed ingester operations for queries triggered by queriers and rulers are now canceled. #3178
 * [BUGFIX] Ruler: directories in the configured `rules-path` will be removed on startup and shutdown in order to ensure they don't persist between runs. #3195
 * [BUGFIX] Handle hash-collisions in the query path. #3192
diff --git a/pkg/chunk/gcp/gcs_object_client.go b/pkg/chunk/gcp/gcs_object_client.go
index 28574373f8a..11421077019 100644
--- a/pkg/chunk/gcp/gcs_object_client.go
+++ b/pkg/chunk/gcp/gcs_object_client.go
@@ -109,8 +109,13 @@ func (s *GCSObjectClient) PutObject(ctx context.Context, objectKey string, objec
 func (s *GCSObjectClient) List(ctx context.Context, prefix, delimiter string) ([]chunk.StorageObject, []chunk.StorageCommonPrefix, error) {
 	var storageObjects []chunk.StorageObject
 	var commonPrefixes []chunk.StorageCommonPrefix
+	q := &storage.Query{Prefix: prefix, Delimiter: delimiter}
+	err := q.SetAttrSelection([]string{"Name", "Updated"})
+	if err != nil {
+		return nil, nil, err
+	}
 
-	iter := s.bucket.Objects(ctx, &storage.Query{Prefix: prefix, Delimiter: delimiter})
+	iter := s.bucket.Objects(ctx, q)
 	for {
 		if ctx.Err() != nil {
 			return nil, nil, ctx.Err()
diff --git a/pkg/ruler/rules/objectclient/rule_store.go b/pkg/ruler/rules/objectclient/rule_store.go
index bbe04235242..834f82d7806 100644
--- a/pkg/ruler/rules/objectclient/rule_store.go
+++ b/pkg/ruler/rules/objectclient/rule_store.go
@@ -6,9 +6,11 @@ import (
 	"encoding/base64"
 	"io/ioutil"
 	strings "strings"
+	"sync"
 
 	"github.com/go-kit/kit/log/level"
 	proto "github.com/gogo/protobuf/proto"
+	"golang.org/x/sync/errgroup"
 
 	"github.com/cortexproject/cortex/pkg/chunk"
 	"github.com/cortexproject/cortex/pkg/ruler/rules"
@@ -26,6 +28,8 @@ import (
 
 const (
 	rulePrefix = "rules/"
+
+	loadRuleGroupsConcurrency = 4
 )
 
 // RuleStore allows cortex rules to be stored using an object store backend.
@@ -74,26 +78,11 @@ func (o *RuleStore) ListAllRuleGroups(ctx context.Context) (map[string]rules.Rul
 		return nil, err
 	}
 
-	userGroupMap := map[string]rules.RuleGroupList{}
-	for _, obj := range ruleGroupObjects {
-
-		user := decomposeRuleObjectKey(obj.Key)
-		if user == "" {
-			continue
-		}
-
-		rg, err := o.getRuleGroup(ctx, obj.Key)
-		if err != nil {
-			return nil, err
-		}
-
-		if _, exists := userGroupMap[user]; !exists {
-			userGroupMap[user] = rules.RuleGroupList{}
-		}
-		userGroupMap[user] = append(userGroupMap[user], rg)
+	if len(ruleGroupObjects) == 0 {
+		return map[string]rules.RuleGroupList{}, nil
 	}
 
-	return userGroupMap, nil
+	return o.loadRuleGroupsConcurrently(ctx, ruleGroupObjects)
 }
 
 // ListRuleGroups returns all the active rule groups for a user
@@ -103,18 +92,12 @@ func (o *RuleStore) ListRuleGroups(ctx context.Context, userID, namespace string
 		return nil, err
 	}
 
-	groups := []*rules.RuleGroupDesc{}
-	for _, obj := range ruleGroupObjects {
-		level.Debug(util.Logger).Log("msg", "listing rule group", "key", obj.Key)
-
-		rg, err := o.getRuleGroup(ctx, obj.Key)
-		if err != nil {
-			level.Error(util.Logger).Log("msg", "unable to retrieve rule group", "err", err, "key", obj.Key)
-			return nil, err
-		}
-		groups = append(groups, rg)
+	if len(ruleGroupObjects) == 0 {
+		return rules.RuleGroupList{}, nil
 	}
-	return groups, nil
+
+	groups, err := o.loadRuleGroupsConcurrently(ctx, ruleGroupObjects)
+	return groups[userID], err
 }
 
 // GetRuleGroup returns the requested rule group
@@ -172,6 +155,54 @@ func (o *RuleStore) DeleteNamespace(ctx context.Context, userID, namespace strin
 	return nil
 }
 
+func (o *RuleStore) loadRuleGroupsConcurrently(ctx context.Context, rgObjects []chunk.StorageObject) (map[string]rules.RuleGroupList, error) {
+	ch := make(chan string, len(rgObjects))
+
+	for _, obj := range rgObjects {
+		ch <- obj.Key
+	}
+	close(ch)
+
+	mtx := sync.Mutex{}
+	result := map[string]rules.RuleGroupList{}
+
+	concurrency := loadRuleGroupsConcurrency
+	if loadRuleGroupsConcurrency < len(rgObjects) {
+		concurrency = len(rgObjects)
+	}
+
+	// Given we store one file per rule group. With this, we create a pool of workers that will
+	// download all rule groups in parallel. We limit the number of workers to avoid a
+	// particular user having too many rule groups rate limiting us with the object storage.
+	g, gCtx := errgroup.WithContext(ctx)
+	for i := 0; i < concurrency; i++ {
+		g.Go(func() error {
+			for key := range ch {
+				user := decomposeRuleObjectKey(key)
+				if user == "" {
+					continue
+				}
+
+				level.Debug(util.Logger).Log("msg", "listing rule group", "key", key, "user", user)
+				rg, err := o.getRuleGroup(gCtx, key)
+				if err != nil {
+					level.Error(util.Logger).Log("msg", "failed to get rule group", "key", key, "user", user)
+					return err
+				}
+
+				mtx.Lock()
+				result[user] = append(result[user], rg)
+				mtx.Unlock()
+			}
+
+			return nil
+		})
+	}
+
+	err := g.Wait()
+	return result, err
+}
+
 func generateRuleObjectKey(id, namespace, name string) string {
 	if id == "" {
 		return rulePrefix