Airlines are selling thousands of seats on Boeing's still-grounded 737 MAX aircraft, betting the planes will be cleared to fly by the time they're scheduled to take off.

American and United are among the airlines that plan to use them for more than 32,600 flights later this year, according to the Sunday Times of London.

A British tourist said he felt like a "guinea pig' when he learned his American Airlines flight to the Caribbean would be on one of the planes. When he bought his ticket, he was assured another jet would be used, and said the airline refused to refund his fare.

The planes were taken out of service after two fatal crashes in a few months. A "travel intelligence specialist' told the Times carriers have begun to reintroduce the planes into upcoming schedules.