For quite some time, Expedia has held the fort as the online one stop shop for holiday planning and buying. That is until now. Booking.com has recently begun performance tests for featuring flights, car rentals and restaurant reservations on the historically accommodation-only site. 

This move will plant the online travel agency in direct competition with Expedia for the first time on a more rounded level. 

Convenience is key when encouraging consumers to book the various elements of their holiday and this was one area in which Booking.com fell down on previously. You could compare hotel rates but when it came to flights you had to go elsewhere. And this is clearly something that Booking.com's parent company Priceline Group has been thinking about for some time. With RentalCars.com, Kayak and OpenTable all under it's helm it was only a matter of time before the opportunity arose to bring the brands together. 

This is purely a test for now, but I'm sure it won't be long until the new tabs are rolled out for the wider public. And, with Expedia recently completing its acquisition of rail technology company SilverRail, they are not resting on their laurels either. 

The gloves are off and it will certainly be interesting to see what happens next.