The three were sentenced Tuesday to caning and jail time. Khong Tam Thanh, Vu Thai Son and Le Michael are British citizens of Vietnamese descent, according to Singapore's Straits Times, which gave their ages as 22, 24 and 24, respectively.
They all pleaded guilty to one charge each of "aggravated outrage of modesty ... while using wrongful restraint," a reduced charge as part of a plea bargain with authorities.
The crime took place early on September 10 in a Singaporean hotel, according to The Straits Times.
The female victim, who has not been named, agreed to go back to a hotel room with a fourth man, according to court documents.
Once she fell asleep, court documents said, the three perpetrators entered the room and sexually assaulted her.
"Purely to obtain sexual gratification, they violated the victim. In doing so, they showed no respect for her dignity or autonomy, and no regard for any harm and hurt they might cause her," Judicial Commissioner Hoo Sheau Peng wrote in her judgment.
"Such conduct is reprehensible."
The men will go to prison for 5½ to 6½ years, based on the judge's assessment of their guilt.
Vu and Thanh will receive eight lashes with a cane, for both their charges, while Le will receive five.