Combustion loses energy(flue gas) which is why BTU output is always less than input on a combustion appliance. Conversely, whatever watts you deliver to an electric heater, that is also it's output. The delivery of those watts as heat may be different, by a fan, just radiant(each may feel different), but nothing changes;1500 watts input results in 1500 watts output. Electric efficiency is 100%.

There is a total difference in cost per btu of electric vs oil, but that too is easy to calculate(watts to btu's). There are neat fuel calculators today that do all the math to make easy comparisons. Except in rare building-point situations, electric radiant is still a cost loser even though it is often the most efficient.