Marine pipeline installation vessel for laying an offshore pipeline in the sea, onto the seabed, said vessel at least being adapted to carry out the reel lay method, wherein the vessel comprises: • a hull and a deck, wherein in the hull a reel well is provided which is located below deck, the reel well being flanked by a left-hand hull section and a right-hand hull section; • a left and a right vertical storage reel (31; 41), arranged adjacent to each other and each with a lower part thereof in the reel well; each storage reel comprising: o a left and right flange (33a, 33b; 43a, 43b); o a hub (34,44) extending between the flanges and being adapted for the storage of a spooled pipeline to be laid, the hub defining a reel rotation axis (32, 42) about which the reel is rotatable; • a left reel support structure provided on the left-hand hull section, and • a right reel support structure provided on the right-hand hull section; • a pipeline launch assembly mounted to the vessel downstream of the reels (31; 41) in a direction of unspooling, which pipeline launch assembly is adapted to launch the unwound pipeline in a firing line into the sea, the pipeline launch assembly comprising: o a pipeline guide adapted to guide unwounded pipeline from the storage reel over the pipeline guide into the firing line; o at least one tensioner provided downstream of the pipeline guide which is adapted for engaging the pipeline in the firing line and supporting at least part of the weight of the launched pipeline to control the rate of laying of the pipeline on the seabed, • an integrally formed common reel support body (40; 50; 60), adapted to support the weight of the two vertical storage reels, the integrally formed common reel support body (40, 50, 60) having a left and right body end (50a, 50b; 60a, 60b) being supported by the left and right reel support structure, respectively, such that the reel support body bridges the reel well and is only supported at its ends on the hull of the vessel; and • left and right bearing structures (46, 47; 52, 53; 62, 63), provided between the reel support body and the left and right storage reels, respectively, characterized in that the integrally formed common reel support body (40, 50, 60) is provided stationary, and in that the integrally formed common reel support body (40, 50, 60) and the left and right bearing structures (46, 47; 52, 53; 62, 63) are adapted to support the two vertical storage reels in a way that the left reel rotation axis and the right reel rotation axis form an obtuse angle (∝). • a hull and a deck, wherein in the hull a reel well is provided which is located below deck, the reel well being flanked by a left-hand hull section and a right-hand hull section; • a left and a right vertical storage reel (31; 41), arranged adjacent to each other and each with a lower part thereof in the reel well; each storage reel comprising: o a left and right flange (33a, 33b; 43a, 43b); o a hub (34,44) extending between the flanges and being adapted for the storage of a spooled pipeline to be laid, the hub defining a reel rotation axis (32, 42) about which the reel is rotatable; o a left and right flange (33a, 33b; 43a, 43b); o a hub (34,44) extending between the flanges and being adapted for the storage of a spooled pipeline to be laid, the hub defining a reel rotation axis (32, 42) about which the reel is rotatable; • a left reel support structure provided on the left-hand hull section, and • a right reel support structure provided on the right-hand hull section; • a pipeline launch assembly mounted to the vessel downstream of the reels (31; 41) in a direction of unspooling, which pipeline launch assembly is adapted to launch the unwound pipeline in a firing line into the sea, the pipeline launch assembly comprising: o a pipeline guide adapted to guide unwounded pipeline from the storage reel over the pipeline guide into the firing line; o at least one tensioner provided downstream of the pipeline guide which is adapted for engaging the pipeline in the firing line and supporting at least part of the weight of the launched pipeline to control the rate of laying of the pipeline on the seabed, o a pipeline guide adapted to guide unwounded pipeline from the storage reel over the pipeline guide into the firing line; o at least one tensioner provided downstream of the pipeline guide which is adapted for engaging the pipeline in the firing line and supporting at least part of the weight of the launched pipeline to control the rate of laying of the pipeline on the seabed, • an integrally formed common reel support body (40; 50; 60), adapted to support the weight of the two vertical storage reels, the integrally formed common reel support body (40, 50, 60) having a left and right body end (50a, 50b; 60a, 60b) being supported by the left and right reel support structure, respectively, such that the reel support body bridges the reel well and is only supported at its ends on the hull of the vessel; and • left and right bearing structures (46, 47; 52, 53; 62, 63), provided between the reel support body and the left and right storage reels, respectively,