Friday is the most expensive day of the week to buy a plane ticket, according to new research, with flights on average 13 per cent dearer than if booked on a Sunday.

Customers have previously been advised to book plane tickets on a Tuesday because they were most likely to find a bargain. Airline executives were said to come into work on a Monday, look at the weekend sales and try to offload the remaining seats on Tuesday.

But according to Greg Schulze, senior vice president of global tour and transport with Expedia, things have now changed.

Airlines Reporting Corporation, the online travel agency which processes tickets booked through travel agencies, studied hundreds of millions of tickets bought in the last 12 months around the world to see the new trends.

Mr Schulze said that there was no clear single day to find the cheapest deal for all fights. However, when flying to most areas of the world, the cheapest tickets were sold on a Saturday or Sunday.

He added that the reason Fridays are so expensive is because airlines launch price hikes then and have already run out of cheap seats.

Airlines are now posting their best deals on weekends because they know that price-conscious consumers will grab them. At the weekend there are also no business travellers looking to get last minute fares which crowds the market.

“I personally would shop at the weekend and the beginning of the week and avoid Friday,” he said.

He added that the days of set airfares are few and far between and that airlines now regularly adjust flight costs up and down.

The research follows statistics from the International Air Transport Association, published last week, that showed how airfares have fallen  year on year.  The American aviation data group also said that customers buying flights in Europe should plan to buy tickets 140 days in advance to get the best price, while those purchasing flights within the US should buy 57 days ahead of departure.

There have been numerous studies into when the best time to book a flight is, with thoughts ranging from as early as possible, to two weeks before, but Rick Seaney, chief executive of price comparison site Fare Compare, said booking too early can be costly.

“Airlines don’t start actively managing the price of seat on a particular flight until about three months before departure for domestic flights and five or six for international trips,” he said. “That’s when price cutting typically begins.”