Outstanding or provision

hey guys 

i have a problem to solve. i m bit comfused between when to make outstanding liabilities and provision.

i  read that we consider an expense as

outstanding liability when amount and payment is certain 

and we make provision for an expense when amount and payment is uncertain(depends on future event but likely to occur)

what we must consider in case either amount or payment, any one thing is uncertain ????

should we make provision or should recognise it as outstanding expense. ?????

here's the case

the electricity bill is recieved in april which is for feb and march.

since we don't know the amount of electricity bill i.e. we can't book it like expense

but since it's certain to occur so i think we should make a provision but m not sure about it.