Esso has resumed operation of its Midline pipeline following repairs and tests.
The pipeline, which transports fuel from the Fawley Refinery in Hampshire to Birmingham Fuel Terminal, had to be closed last week after a tapping device was found inserted into it.
The device was discovered near an industrial storage unit at West Wellow, Romsey, in Hampshire, where 30,000 litres of diesel, believed to have been stolen from the pipeline, was recovered.
Hampshire police said two men, both from the Salisbury area, were arrested on suspicion of conspiracy to steal fuel, and have been bailed until July 10, pending further enquiries.
During the shutdown alternative supply arrangements were put in place, and Esso said it did not anticipate any impact on its retail customers.