[AccessD] Problem with IIF statement

[Kaup, Chester]

I have the following IIF statement

ProducerCount: IIf(Nz([Oil],0+Nz([Wtrp],0)+Nz([HCGas],0)+Nz([Co2P],0))>0,1,0)

The value of Oil, Wtrp and CO2P are 0. The value of HCGas is 7258. The result of the IF statement is 0

I tried adding all 4 values together and got a sum of 7258. All values are defined a type double in the source table.

I don't understand what is happening. Maybe there is a better way to write the query.

Thanks for your assistance.