(Repeats story published on May 15 with no changes to text)

* Fleet of tankers grows offshore due to lack of dollars

* Government lifts cap on fuel prices at pumps

* Unions call for strike in protest against price rises

* Delta unrest cuts oil output, makes gasoline swaps tougher

By Libby George and Chijioke Ohuocha

LONDON/LAGOS, May 15 (Reuters) - The growing fleet of tankers stuck off Nigeria unable to unload their cargoes of diesel and petrol is an even-present reminder for President Muhammadu Buhari that another fuel crisis is looming on the horizon.

At least 75 ships with two and a half million tonnes of fuel are waiting for importers in Africa's biggest economy to find the dollars they need to pay for the cargoes, according to ship tracking data and fuel traders.

Some of the vessels arrived a month ago and their frustrated owners have almost given up hope and started to offer their fuel to buyers outside Nigeria, several traders told Reuters.

A slump in world oil prices has hammered Nigeria's state income and because crude sales are the government's main source of revenue the fall has caused crippling shortages of dollars within the economy that have been hurting businesses for months.

In a bid to break the impasse and head off more fuel shortages, the government raised the price cap for petrol by 67 percent, officially sanctioned importers to use the black market to find the hard currency they need to get cargoes off the ships and allowed any Nigerian company to import fuel.

Announced last week, the reforms were welcomed by some in the oil industry as badly needed steps in the right direction. The changes have largely eliminated the system of heavily subsidised fuel prices, removing one strain on Nigeria's increasingly stretched finances.

But the so-called parallel market has struggled to cope with the demand for U.S. dollars that followed the reforms.

Nigeria consumes 45 million litres of gasoline a day, or roughly 280,000 barrels, which would require the market to provide some $18 million a day. Though importers cover about 30 percent of this, with the state oil firm covering the rest, it is still a big strain on the market for dollars.

The naira has already weakened due to the spike in demand for dollars from fuel importers. Last week, the U.S. currency fell to 324 naira on the parallel market, whereas the official exchange rate has been held firm just under 200.

"The risk is that the parallel rate will depreciate even more, giving the marketers a pretext for yet further price increases at the pump," said Alan Cameron, an economist covering Africa with Exotix Partners.