The airport package will be placed in trains bound for Gatwick, Stansted and Luton through KBH's contract with train operator FCC Thameslink, which services Gatwick and Luton, and its recent Stansted Express concession win.
More than five million travellers a year use the Stansted Express.
The City-focused ads will appear on onboard panels on commuter trains arriving at Moorgate, Liver-pool Street and Fenchurch Street.
Both packages will be available to advertisers for two-week campaigns.
Ian Reynolds, managing director of KBH, believes the onboard packages will appeal to advertisers who are trying to get the most out of their money.
"We believe these extremely targeted packs will help adver- tisers zone in on these valuable audiences in very cost-effective ways," he said.
KBH Transport Media holds the contracts to advertise on trains belonging to nine operators, including Silverlink, First Great Western Link and South West Trains.