A 24-year-old man was jailed for seven months on Tuesday after pleading guilty to the offence of having oral sex with an underage girl.

Muhammad Hairuniezam Marwi, who was then 22 when he committed the offence on July 9, 2012, saw a friend of his having sex with the 15-year-old girl behind the walls at a skate park beside *Scape along Somerset Road and asked her for oral sex, a district court heard on Tuesday.

Hairuniezam, who is a dance instructor, could have been jailed for up to 10 years and/or fined for the offence.

Deputy Public Prosecutor Elizabeth Chua told the court that the girl joined a group of people including Hairuniezam and his friend, Ryan Nicholas Shah, 27, at the skate park that evening. The group started drinking an alcoholic cocktail. The victim drank several glasses and began to feel intoxicated.

At about 11pm, Shah and the girl went behind one of the walls at the park to urinate.

After some time, Hairuniezam went to check on them as they had not returned. He found the pair having sex behind one of the walls. He approached the victim and asked her to perform oral sex on him and she did.

At about midnight, the two men sent the victim home in a taxi.

The victim's mother was worried when she saw them. She later found the girl lying on the ground at the front door of the house. The victim then told her mother that she had had sex with the men. Her parents called the police.

The victim's blood and urine samples were analysed and found to contain a high level of ethanol.

Shah, who has been charged with having sex with the girl, will return to court on Feb 24 for his case to be mentioned.