Fewer people are being found guilty of sham marriages after laws were enacted to tackle the problem of foreigners paying Singaporeans to marry them - so they could stay on in Singapore.
Last year, 170 people were convicted of being involved in a marriage of convenience, down from 284 in 2013.
From January to May this year, 34 people were convicted, the Immigration and Checkpoints Authority (ICA) told The Straits Times.
The ICA's Assistant Superintendent Yeo Ting Haw, from the enforcement division, attributed the drop in numbers to the law having a deterrent effect.
In 2012, it became a criminal offence to arrange or enter into a sham marriage. Culprits face up to 10 years' jail or a fine of up to $10,000, or both.
Before the law was passed, those suspected of being part of a sham marriage could be charged only with giving false information to the authorities, an offence which carries a penalty of up to one year in jail, a fine of up to $4,000, or both.
The tougher law has deterred would-be offenders.
One matchmaker said he used to get women from China asking him to arrange such sham marriages in the past, but those calls have since stopped. "It is not worthwhile to risk going to jail for a few thousand dollars," he said.
ASP Yeo said that most of the foreigners involved in the sham marriages are women in their 20s and 30s from China and Vietnam, and some men from India.
They often come to Singapore as tourists and want to stay on to find work for themselves.
Some are already working illegally, often in the vice trade.
The foreigners pay the middlemen up to $26,000 to arrange a marriage of convenience for them.
The Singaporeans are often men in their 30s to 70s, who are strapped for cash.
They are usually paid between $2,000 and $5,000 for marrying a foreigner, but some do the job for as little as a few hundred dollars.
The ICA gets tip-offs about these bogus unions. Its officers also probe suspicious couples.
For example, the man may be very much older than his wife.
Or their accounts of their lives together do not match.
ASP Yeo said: "Most of these cases were cracked when we interviewed the couple separately."
In most such cases, the couple live separately.
But some of the women offer sex to their so-called husbands to keep them happy.
ASP Yeo said there are also men who pay their wives to have sex, as sex was not part of their agreement and the women are working as prostitutes.
The ICA has also seen a few cases of middlemen approaching poor or retired elderly Singaporean men to ask them whether they were keen to take a foreign bride.
The men were not paid as they thought they were really getting a wife, ASP Yeo said, but the foreigners had no intention of settling down.
These women often disappeared from the lives of their husbands shortly after tying the knot, but not before getting a work permit or a long-term visit pass.
ASP Yeo said: "Some of these poor men were still hoping their wives would go back to them."
He added that the ICA will spare no effort to go after sham-marriage offenders and urged the public to report any suspicious individuals to the ICA at 1800-391-6150.