UK property portal OnTheMarket will boost its marketing and advertising spend sixfold if a bid to buy it by US-based CoStar Group goes ahead.

AIM Group’s Ben Salisbury reported today that CoStar had agreed to buy OnTheMarket for £100 million (A$191.9 million).

The property data vendor and marketplace operator has offices in 15 countries and is valued at US$40 billion.

Salisbury says the deal will put CoStar in a position to challenge Zoopla and Rightmove’s dominance in the UK, as it bids to become the market’s number one portal.

The board of OnTheMarket has unanimously recommended acceptance of the offer, and CoStar has received irrevocable undertakings and letters of intent regarding the 29.5 per cent of OnTheMarket shares from its six largest shareholders, among them realtor group Spicerhaart.

OnTheMarket “will spend six times more than it currently does on marketing and advertising and more than three times the current annual media spend of Rightmove,” according to the statement.