operating expense and operational expense.
Faced with the increase in oil prices, we must save the operating expenses through reduction of a heating cost.

Is "operational expenses" also acceptable instead of "operating expenses"?

Question

operating expense and operational expense.
Faced with the increase in oil prices, we must save the operating expenses through reduction of a heating cost.

Is "operational expenses" also acceptable instead of "operating expenses"?

Answer

Yes, to me both are fine, but you have a couple of other errors:
You should not have 'the' before operating/ional - as you have not defined which expense 'the' is referring to.
Similarly you should not have 'a' before heating, as it is highly unlikely you can simply eliminate one specific cost. It probably should be 'of heating costs'.