i heard from cartrade com that maruthi is going to launch

i heard from cartrade.com that maruthi is going to launch CNG version for 5 models like ALTO,WAGON R,EECO,SX4.Estillo.i need to know is that the maintainence cost and running costof these CNG vehicles are similar to that of Diesel vehicle or it is costlier than Diesel model vehicle.i need to know what is CNG is that it runs in Gas or petrol,which is advantage CNG or Diesel for Maintaince and Running cost.if CNG is better pls do tell me out of 5 models like ALTO,WAGON R,EECO,SX4,Estillo which is better to buy.waiting for your reply shiva