Ryanair chief executive Michael O'Leary expects European airfares to rise sharply over the next 12 months. He described the expected increase as the biggest in European aviation history. According to O'Leary, ticket prices could climb by as much as 20 percent. The airline boss linked the forecast to higher costs for jet fuel. His warning indicates that budget carriers may pass more of their fuel bill on to passengers. The forecast covers a full year and includes the peak summer travel period, when demand for low-cost flights is usually strong. The 20 percent figure is a ceiling in his warning, not a promise that every route or ticket will become more expensive by that amount.