That includes estimates on how much energy they used during winter 2016/17 and the accuracy of the annual consumption figures given to customers in their annual statements.
The regulator will examine whether OVO Energy breached licence conditions related to giving information that is accurate or based on a best estimate, complete and not misleading.
Ofgem said: “Incorrect consumption figures can lead to customers receiving inaccurate bills, annual statements and other important information. This in turn can lead to customers being unable to properly manage their accounts and deciding to switch based on incorrect information.”
However, it added the opening of this investigation does not imply the regulator has made any findings about non compliance by the supplier.
An OVO Energy spokesperson said: “We have a great track record in customer service and are always open to ways to improve it.”