Sydney drivers have been told it's too late to fill up cheaply before the long weekend, with petrol prices set to hit an 11-year-high.

The average price for petrol is expected to reach 166 cents a litre on Wednesday and won't begin to drop again until next week, the NRMA says.

Sydney motorists have been warned to expect high petrol prices this long weekend. Credit:James Davies

Spokesman Peter Khoury said the increased volatility of world oil prices is to blame and Australia is "hugely exposed".

"We knew the attacks in Saudi Arabia, along with the ongoing trade war between the United States and China and a weaker Australian dollar would all work against our members here at home and we are now confronted with 11-year-high prices just as families are going away," Mr Khoury said.