Realising he was about to break the law by paying for sex with an underaged girl, Qiu Wenbo tried to get around it by obtaining only oral sex from the 17-year-old before running off without paying.

This cut no ice with a district court who heard his account and the 28-year-old was on Monday sentenced to six months in jail for the offence, and another month for two unrelated offences.

Qiu, who is also known as Allan Khoo Wenbo, became the 27th of 51 men charged last year with paying the same girl for sex to receive punishment, in a long-running online vice ring case.

On Dec 23, 2010, Qiu was to pay the girl $650 for sexual services.

While the girl was taking a shower, Qiu checked her identity card which was in her wallet and realised she was underaged.

Aware that it would be an offence to pay her for sex, he asked to receive only oral sex from her. After the act, she took another shower to clean up, and Qiu fled without paying while she was in the bathroom.

He pleaded guilty yesterday to the offence and two charges of using another person's identity card to gain access to the Marina Bay Sands casino in December 2011. One charge of failing to pay an entry levy to the casino was taken into consideration.

The maximum penalty for the sex offence is seven years in jail and a fine.