Ryanair reported a fall in its seat occupancy or load factor in February compared to the same month last year.
Ryanair said its February load factor - which measures the proportion of seats filled - slipped to 77 per cent from 81 per cent in February 2003.
The four percentage point decline compared with a fall of five percentage points in January.
The airline said passenger traffic grew by 45 per cent to 1.9 million in February versus the same month last year.
Analysts said they expected little let-up in pressure on the airline's load factor while it adds new routes and more planes, in a bid to boost annual passenger volume by 50 per cent to 24 million this year. Ryanair has opened two new European bases in Rome and Barcelona since the start of 2004.
"This (expansion) is due to slow down from May and we should see load factors stabilising then before starting to improve," said Mr John Mattimoe, analyst at Merrion Stockbrokers.
Load factors by then will also benefit, in year-on-year comparisons, from the lower base in year-ago figures, he added.
Investor confidence in Ryanair was shaken by a shock profit warning last month, when the airline said annual profit could fall as much as 10 per cent as it slashes ticket prices to fill seats in the face of tough competition.
"Yield trends remain the critical issue and will determine future investor interest," added Mr Mattimoe. Yield refers to average revenue per passenger carried.
At 2 p.m. Ryanair shares were trading 0.6 per cent lower at €4.87 on the Irish Stock Exchange.