Described herein is a fuel supply system (1) for an internal combustion engine (3). The fuel supply system (1) includes a fuel tank (2), a fuel distribution manifold (5), and a pumping unit (6). The pumping unit (6) connects together the fuel tank (2) and the fuel distribution manifold (5). The pumping unit (6) includes a fluid line (11) having a low-pressure portion (P1), a high-pressure portion (P2), a high-pressure pump (9) connecting together the low-pressure portion (P1) and the high-pressure portion (P2), and a pre-feed pump (8) connected to the low-pressure portion (P1). Further, the low-pressure portion (P1) includes a plurality of low-pressure branches (23-28, 30-34), a plurality of fluid components (8, 13, 21, 29,.231, 232, 233, 241, 242, 251, 261, 271, 311), and at least one tubular coupling (40, 140, 340, 440). Each of the fluid components (8, 13, 21, 29, 231, 232, 233, 241, 242, 251, 261, 271, 311) has at least one connector (36). Further, each tubular coupling (40, 140, 340, 440) includes a plastic tubular body (145, 345, 445), a sealing unit (41, 141, 341, 441) interposed between the tubular body (145, 345, 445) and the corresponding connector (36), and connecting units (42, 142, 342, 442) for axial locking of the tubular body (145, 345, 445) with respect to the connector (36) in a defined axial position.
