SINGAPORE - A 32-year-old man who was convicted after trial of engaging in commercial sex with a social escort in the high-profile online vice ring case was sentenced to 16 weeks in jail on Monday.

But Koh Zi Yang is appealing against conviction, and was offered bail of $20,000.

District Judge Shaiffudin Saruwan found him guilty of paying $650 for the sexual services of the minor at Strand Hotel in Bencoolen Street on Dec 23, 2010.

A total of 51 men were charged with having paid sex with the 17-year-old escort, who was working for pimp Tang Boon Thiew from September 2010 to February 2011.

Tang, 41, who operated the vice ring, has been jailed for four years and 10 months and fined $90,000 for vice-related offences.

The prosecution's case is that Koh contacted the pimp on Dec 23, 2010 and booked the minor for sex after agreeing to pay $650 for her sexual services.

On the same day, the minor performed oral sex on Koh and also engaged in sexual intercourse with him in the hotel room.

But Koh claimed in his defence that he had "premature ejaculation'' and had a tendency to ejaculate too early. This was what happened in the hotel room when the minor was caressing him.

The prosecution argued that his account was fabricated and entirely at odds with the available evidence.

Even though the minor, now 21, could not pick out Koh's photograph during investigation nor identify him in court, the prosecution said there was no prospect of mistaken identity due to the significant lapse in time since the offence was committed.

The minor had said that she served between 50 and 80 clients when she was working for Tang. Most of them engaged her for sexual services.

Koh, who helps in his family business, could have been jailed for up to seven years and/or fined for paid sex with a person under 18 years old.

To date, only two men have been acquitted of having paid sex with this minor.