The 24-year-old man was attacked at around 9.30pm while relieving himself in a bush on the edge of the Theresienwiese field where the Oktoberfest is held.
A man came up to him and said he wanted to have sex with him, police said on Sunday.
The 24 year-old rejected the advance. He was then attacked from behind and forced to the ground. One man held him down while another man raped him.
Police said the unknown men then fled. Police confirmed to The Local the victim was a British tourist but would not confirm reports he was from Leeds.
Officers added that despite the horrific attack, sex crimes were down at this year’s Oktoberfest so far.
There have been seven reported sexual assaults, including two rapes, compared to 12 sex attacks over the same period last year.
Figures for the first week of Oktoberfest showed that overall crime has also fallen on the previous year, with 659 crimes reported, compared with 831 in 2013 - a drop of 20 percent.
Key figures include:
- 37 fewer violent crimes than last year at 202
- 235 people arrested
- Pickpocketing down, with 212 cases reported compared with 284 in 2013
- 39 pickpockets arrested
- 111 people arrested for drugs offences
- 350 people treated for alcohol illnesses
Police also said that attacks using the heavy glass beer mugs (Maß), stood at 15 compared to 37 last year.
Some of the decrease in crime was attributed to lower visitor numbers than last year.
Arrests include a 27-year-old Italian who was held on Friday for a knife attack. A 20-year-old man was dancing on a bench and table adjacent to the Italian. The 20 year-old then fell off the table, taking other people with him.
The Italian responded by grabbing a bread knife and injured the man in the back.
And on Saturday at 2pm, a 25-year-old American soldier rampaged through one of the marquees, police said.
He was taken into custody by a group of security guards.
On his way to the Oktoberfest’s temporary police station he started screaming “Nazis” at the security guards. He then bit a police officer on the left arm.
He was handed over to US military police.
A total of 3.3 million people had passed the gates of the Theresienwiese by Saturday evening, compared with 3.5 million in the first week of Oktoberfest 2013.
Those visitors have so far drunk 3.2 million litres of beer.
Munich Red Cross said its medics had treated 3,737 people, of whom 1,902 required attention from a doctor.
Visitors turned to the Red Cross with complaints ranging from sore throats to surgical emergencies.