The low cost carrier reported a pre-tax loss of £153m for the six months to 31 March, up from £79m a year earlier.
Rising oil prices, cautious consumers and higher passenger taxes were blamed for the widening losses.
Fuel costs totalled £43m in the period, the company adds, while passenger duties cost £21m.
Revenue increased 8.1% to £1.3bn for the half-year, lifted by an 11.6% increase in passenger numbers to 23.9 million.
Chief executive Carolyn McCall says that despite a “tough” first-half, the company is making “strong progress”.
McCall set out her strategy to grow the business, including targeting business travellers and introducing more flexible fares, in November.
The airline was given licence to exploit the easyJet brand following settlement of its long-running legal battle with founder Stelios Haji-Ioannou that allowed it to retain the brand and have “greater commercial flexibility”.
It wants to add marketing partnerships, such as the agreement recently signed with Nectar, to increase awareness of its offerings.
In the results statement, the company says it is “in negotiations across Europe to secure further agreement to generate additional marketing support”.