FOR Samwoo Ee, the first bet was just a warm-up.

Mr. Ee, 30, worked at an Internet company in SoHo, and had been competing with a colleague to see who could lose more weight. But they had both stopped going to the gym because of long hours at the office. In search of more motivation, they turned up the pressure: they entered into a formal one-month wager to see who could cut the higher percentage of their body mass index.

“It got pretty competitive,” said Mr. Ee, who weighed 248 at the time. “We used to do push-ups every hour in front of each other’s cubicles. And he used to leave really good chocolate on my desk.”

His co-worker, Daniel Fries, won the first month, after losing about 16 pounds to Mr. Ee’s 10, and Mr. Ee paid him $20.

Then, Mr. Ee said, “it got serious.”

Six co-workers joined them in another weight-loss competition. “I told them this was going to be dirty,” Mr. Ee said. There were weekly weigh-ins by an outside record keeper. Mr. Ee finished second in that bet, after losing an additional four pounds. Along the way, Mr. Ee’s officemates enjoyed taunting one another with comments like, “Are you sure you want to eat that bagel?” and “Why don’t you get a cheeseburger for lunch and I’ll get a salad?”