Ryanair chief executive Michael O'Leary has said the airline's earnings forecast for the current financial year has not changed.
But he told reporters fuel costs would be higher than expected if oil prices remained at record highs, adding that Ryanair's rivals would also be forced to increase their fuel surcharges and raise fares.
He said every $1 rise in fuel costs above $47 a barrel would wipe €5m off annual pre-tax profits. Ryanair is unhedged on fuel until September, when it is hedged at $47 a barrel.
Meanwhile, Ryanair has announced four new routes to France, Lithuania and Poland. The new routes, which will start in September and October, will run daily from London-Stansted to Grenoble, Kaunas, Lodz and Poznan.
Ryanair will be the first low-cost airline to fly into and out of Lithuania in September. The airline plans to carry some 100,000 pasengers a year on the new route. Lithuania joined the European Union last year.
In February the Lithuanian government sent letters to eight low-cost European airlines inviting them to begin service to the Baltic state, but only received a reply from Ryanair.
Ryanair has also increased the frequency on its existing routes from London Stansted to Derry, Seville, Granada, Riga and Tampere.
Ryanair shares closed three cent lower at €6.30 in Dublin this evening.