On Friday the atheist bus campaign attracted 57 complaints from members of the public and religious groups, but by this morning that figure has more than doubled to 116.
The Advertising Standards Authority is still in the process of logging complaints and deciding whether to launch an investigation.
The majority of people complained the ad is offensive to Christians and other religions.
It is thought that the question of whether God exists will be considered a subjective issue under ASA guidelines so will not merit an investigation.
One of those to complain to the ASA is Stephen Green, of Christian Voice, who has challenged the ads on grounds of "truthfulness" and "substantiation", suggesting that there is not "a shred of supporting evidence" that there is probably no god.
The campaign was launched following an appeal by a Guardian newspaper blogger, Ariane Sherine, who challenged readers to raise enough funds to run an ad telling people "there's probably no god" on a single central London bus route.
The campaign, which carries the line "There's probably no god. Now stop worrying and enjoy your life", was brokered through outdoor media company CBS Outdoor.