CHICAGO — Starting Aug. 1, passengers who get the midair munchies on select United Airlines flights will be able to buy chips, cookies, candy and trail mix, all for $3 apiece.

What will $3 get you? Jumbo-size snacks, weighing 4 to 5 ounces, that previously weren't available onboard the Chicago-based carrier's flights.

United, the nation's second-largest airline, behind American Airlines, will test the new service on Chicago-Denver and Chicago-Boston flights, plus a handful of other routes.

In addition, United raised the price of alcoholic beverages for passengers flying coach in the U.S. by $1, to $6, as of Tuesday, and it plans to roll out a $1 price increase on Pacific and intra-Asia flights Aug. 1.

The changes in United's onboard service were announced to employees in a memo this week and confirmed by a spokeswoman.

United still will distribute half-ounce bags of pretzels, its standard onboard snack, free to penny-pinching passengers. And its assortments of sodas and juices will remain free for now, although United won't rule out charging for them in the future, said spokeswoman Robin Urbanski.

US Airways, a United partner in the Star Alliance, plans to begin charging $2 for onboard sodas as of Aug. 1 and $7 for alcoholic libations.

United and other carriers are seeking new ways to make money as they struggle to raise airfares sufficiently to cover rising fuel costs. Delta Air Lines and Northwest Airlines, for example, already sell onboard snacks for $3.

United believes it eventually can generate $1 billion annually from a plethora of new fees and services, Urbanski said. The concept is to introduce a menu of a la carte services to passengers, who then pay for items they truly want or need.

Some of the offerings weren't previously for sale to passengers, such as cookies or seats in United's roomier Economy Plus section. Others will leave passengers paying for things that most used to take for granted, like checking luggage.

The strategy, adopted by most major U.S. carriers, could backfire if irate passengers defect to rival Southwest Airlines, a holdout that mocks the fees in a new ad campaign.

"The question is how many of those travelers do they send over to their competitor, Southwest?" asked Tom Parsons, head of www.BestFares.com.