The Californian company admitted that 11 minor accidents took place over more than one million miles in self-driving mode.
Director of Google's self-driving car project Chris Urmson wrote in a blog post that all 11 accidents involved "light damage" and "no injuries".
"Not once was the self-driving car the cause of the accident," he wrote.
Google has so far outfitted 23 Lexus SUVs with driverless technology.
The search giant's driverless vehicles have already clocked 1.7million miles (around 2.8million kilometres) of testing on US roads.
In this time, Google cars have been rear-ended seven times – often when at a stop – "but also on the freeway," Mr Urmson confirmed in the official blog.
Other Google cars had been side-swiped or "hit by a car rolling through a stop sign."
Google self driving vehicles have already clocked 1.7million miles of real-world tests on US roads
Eight of the 11 collisions were on city streets, he revealed.
Mr Urmson also described instances in which Google's cars avoided hitting other cars or cyclists as they drove on streets near the company's Silicon Valley headquarters.
Nevada, Michigan and Florida have passed laws welcoming tests of self-driving cars onto their roads.
California's regulators provided the total – four accidents since September – but would not comment about their exact nature or severity.
Regulators cited a longstanding Californian state law which makes all collision reports confidential.
However, some details were revealed by a person familiar with these reports.
Speaking anonymously to the Associated Press, the source revealed that two of the accidents happened while the cars were in self-driving mode.
In the other two, the person required to be behind the wheel was in control.
All four happened when the test car was moving at speeds of less than 10 mph (around 16 kph), said the person.
One of the key selling points for self-driving vehicles is the perceived increase in safety.
Their cameras, radar and laser sensors provide a far more detailed understanding of their surroundings than humans have – and reaction times should be faster.
Cars can be programmed to adjust if they sense a crash coming – move a few feet, tighten seat belts, honk the horn or flash lights at a distracted driver.
"Even when our software and sensors can detect a sticky situation and take action earlier and faster than an alert human driver, sometimes we won't be able to overcome the realities of speed and distance," Google's Urmson wrote.
"Sometimes we'll get hit just waiting for a light to change."
