diff --git a/GNNGraphs/src/GNNGraphs.jl b/GNNGraphs/src/GNNGraphs.jl
index 1c4947d45..783d98b15 100644
--- a/GNNGraphs/src/GNNGraphs.jl
+++ b/GNNGraphs/src/GNNGraphs.jl
@@ -75,7 +75,7 @@ export add_nodes,
        rand_edge_split,
        remove_self_loops,
        remove_edges, 
-       remove_multi_edges,
+       coalesce,
        set_edge_weight,
        to_bidirected,
        to_unidirected,
diff --git a/GNNGraphs/src/deprecations.jl b/GNNGraphs/src/deprecations.jl
index d6a8e1797..04273cf4d 100644
--- a/GNNGraphs/src/deprecations.jl
+++ b/GNNGraphs/src/deprecations.jl
@@ -11,3 +11,5 @@ function Base.getproperty(vds::Vector{DataStore}, s::Symbol)
         return [getdata(ds)[s] for ds in vds]
     end
 end
+
+@deprecate remove_multi_edges(g::GNNGraph{<:COO_T}; aggr = +) Base.coalesce(g; aggr = aggr)
\ No newline at end of file
diff --git a/GNNGraphs/src/gnngraph.jl b/GNNGraphs/src/gnngraph.jl
index 0a818b4d2..b90cfc032 100644
--- a/GNNGraphs/src/gnngraph.jl
+++ b/GNNGraphs/src/gnngraph.jl
@@ -113,6 +113,20 @@ struct GNNGraph{T <: Union{COO_T, ADJMAT_T}} <: AbstractGNNGraph{T}
     ndata::DataStore
     edata::DataStore
     gdata::DataStore
+    is_coalesced::Bool # only for :coo, true if the graph is coalesced, i.e., indices ordered by row and no multi edges
+end
+
+# GNNGraph constructor setting the is_coalesced field to false
+function GNNGraph(graph::T,
+                  num_nodes::Int,
+                  num_edges::Int,
+                  num_graphs::Int,
+                  graph_indicator::Union{Nothing, AVecI},
+                  ndata::DataStore,
+                  edata::DataStore,
+                  gdata::DataStore) where {T <: Union{COO_T, ADJMAT_T}}
+    return GNNGraph{T}(graph, num_nodes, num_edges, num_graphs,
+                       graph_indicator, ndata, edata, gdata, false)
 end
 
 function GNNGraph(data::D;
diff --git a/GNNGraphs/src/query.jl b/GNNGraphs/src/query.jl
index b427c5916..e2e5f9bdb 100644
--- a/GNNGraphs/src/query.jl
+++ b/GNNGraphs/src/query.jl
@@ -103,6 +103,18 @@ Graphs.ne(g::GNNGraph) = g.num_edges
 Graphs.has_vertex(g::GNNGraph, i::Int) = 1 <= i <= g.num_nodes
 Graphs.vertices(g::GNNGraph) = 1:(g.num_nodes)
 
+"""
+    is_coalesced(g::GNNGraph) -> Bool
+
+Check whether the given `GNNGraph` `g` is coalesced (see [`coalesce`](@ref)). Only meaningful for COO graphs.
+
+# Arguments
+- `g::GNNGraph`: The graph to check.
+
+# Returns
+- `Bool`: Whether the graph is coalesced. If the graph is not of type COO, this function will always return `false`.
+"""
+is_coalesced(g::GNNGraph) = g.is_coalesced
 
 """
     neighbors(g::GNNGraph, i::Integer; dir=:out)
diff --git a/GNNGraphs/src/transform.jl b/GNNGraphs/src/transform.jl
index afc94b517..ce8d90b6a 100644
--- a/GNNGraphs/src/transform.jl
+++ b/GNNGraphs/src/transform.jl
@@ -44,7 +44,7 @@ end
 Return a graph constructed from `g` where self-loops (edges from a node to itself)
 are removed. 
 
-See also [`add_self_loops`](@ref) and [`remove_multi_edges`](@ref).
+See also [`add_self_loops`](@ref) and [`coalesce`](@ref).
 """
 function remove_self_loops(g::GNNGraph{<:COO_T})
     s, t = edge_index(g)
@@ -146,15 +146,14 @@ function remove_edges(g::GNNGraph{<:COO_T}, p = 0.5)
 end
 
 """
-    remove_multi_edges(g::GNNGraph; aggr=+)
+    coalesce(g::GNNGraph; aggr=+)
 
-Remove multiple edges (also called parallel edges or repeated edges) from graph `g`.
-Possible edge features are aggregated according to `aggr`, that can take value 
-`+`,`min`, `max` or `mean`.
+Return a new GNNGraph where all multiple edges between the same pair of nodes are merged (using aggr for edge weights and features), and the edge indices are sorted lexicographically (by source, then target).
+This method is only applicable to graphs of type `:coo`.
 
-See also [`remove_self_loops`](@ref), [`has_multi_edges`](@ref), and [`to_bidirected`](@ref).
+`aggr` can take value `+`,`min`, `max` or `mean`.
 """
-function remove_multi_edges(g::GNNGraph{<:COO_T}; aggr = +)
+function Base.coalesce(g::GNNGraph{<:COO_T}; aggr = +)
     s, t = edge_index(g)
     w = get_edge_weight(g)
     edata = g.edata
@@ -181,7 +180,7 @@ function remove_multi_edges(g::GNNGraph{<:COO_T}; aggr = +)
     return GNNGraph((s, t, w),
              g.num_nodes, num_edges, g.num_graphs,
              g.graph_indicator,
-             g.ndata, edata, g.gdata)
+             g.ndata, edata, g.gdata, true)
 end
 
 """
@@ -441,7 +440,7 @@ end
     to_bidirected(g)
 
 Adds a reverse edge for each edge in the graph, then calls 
-[`remove_multi_edges`](@ref) with `mean` aggregation to simplify the graph. 
+[`coalesce`](@ref) with `mean` aggregation to simplify the graph. 
 
 See also [`is_bidirected`](@ref). 
 
@@ -505,7 +504,7 @@ function to_bidirected(g::GNNGraph{<:COO_T})
                  g.graph_indicator,
                  g.ndata, edata, g.gdata)
 
-    return remove_multi_edges(g; aggr = mean)
+    return coalesce(g; aggr = mean)
 end
 
 """
@@ -525,7 +524,7 @@ function to_unidirected(g::GNNGraph{<:COO_T})
                  g.graph_indicator,
                  g.ndata, g.edata, g.gdata)
 
-    return remove_multi_edges(g; aggr = mean)
+    return coalesce(g; aggr = mean)
 end
 
 function Graphs.SimpleGraph(g::GNNGraph)
diff --git a/GNNGraphs/test/transform.jl b/GNNGraphs/test/transform.jl
index 275efe006..256d851bf 100644
--- a/GNNGraphs/test/transform.jl
+++ b/GNNGraphs/test/transform.jl
@@ -345,7 +345,7 @@ end
     end
 end
 
-@testitem "remove_multi_edges" setup=[GraphsTestModule] begin
+@testitem "coalesce" setup=[GraphsTestModule] begin
     using .GraphsTestModule
     for GRAPH_T in GRAPH_TYPES
         if GRAPH_T == :coo
@@ -353,14 +353,14 @@ end
             s, t = edge_index(g)
             g1 = add_edges(g, s[1:5], t[1:5])
             @test g1.num_edges == g.num_edges + 5
-            g2 = remove_multi_edges(g1, aggr = +)
+            g2 = coalesce(g1, aggr = +)
             @test g2.num_edges == g.num_edges
             @test sort_edge_index(edge_index(g2)) == sort_edge_index(edge_index(g))
 
             # Default aggregation is +
             g1 = GNNGraph(g1, edata = (e1 = ones(3, g1.num_edges), e2 = 2 * ones(g1.num_edges)))
             g1 = set_edge_weight(g1, 3 * ones(g1.num_edges))
-            g2 = remove_multi_edges(g1)
+            g2 = coalesce(g1)
             @test g2.num_edges == g.num_edges
             @test sort_edge_index(edge_index(g2)) == sort_edge_index(edge_index(g))
             @test count(g2.edata.e1[:, i] == 2 * ones(3) for i in 1:(g2.num_edges)) == 5
@@ -714,3 +714,51 @@ end
         end
     end
 end
+
+@testitem "graph transform ops set is_coalesced=false" setup=[GraphsTestModule] begin
+    using .GraphsTestModule
+    g = rand_graph(5, 10, graph_type=:coo)
+    g = coalesce(g)  # ensure the graph is coalesced to start with
+
+    # add_self_loops
+    g1 = add_self_loops(g)
+    @test g1.is_coalesced == false
+
+    # remove_self_loops
+    g2 = add_self_loops(g)  # ensure there are self-loops to remove
+    g2 = remove_self_loops(g2)
+    @test g2.is_coalesced == false
+
+    # remove_edges
+    g3 = remove_edges(g, [1])
+    @test g3.is_coalesced == false
+
+    # add_edges
+    g4 = add_edges(g, [1], [2])
+    @test g4.is_coalesced == false
+
+    # perturb_edges
+    g5 = perturb_edges(g, 0.5)
+    @test g5.is_coalesced == false
+
+    # remove_nodes
+    g6 = remove_nodes(g, [1])
+    @test g6.is_coalesced == false
+
+    # add_nodes
+    g7 = add_nodes(g, 2)
+    @test g7.is_coalesced == false
+
+    # rand_edge_split returns two graphs
+    g8a, g8b = rand_edge_split(g, 0.5)
+    @test g8a.is_coalesced == false
+    @test g8b.is_coalesced == false
+
+    # negative_sample
+    g9 = negative_sample(g, num_neg_edges=3)
+    @test g9.is_coalesced == false
+
+    # ppr_diffusion
+    g11 = ppr_diffusion(g)
+    @test g11.is_coalesced == false
+end