What would be the GDP of Algeria without Oil & Gas? Facts :

*Algeria's GDP is 230 B$,
*Oil &amp; Gas account for 30% (70 B$)


My simplistic reasoning would say : Substract 70 from 230 and get a new GDP of 160 B$.

But I know that the concept of GDP is more complex than that: it also includes government spending :

*Government consumption accounts for 30% (70 B$)
*60% of the budget comes from Oil &amp; Gas : 42 B$


So I'll continue substracting: 160 - 42 = 118 B$, the new GDP...

But still, I think it's too high: the household consumption accounts for 35%. Most purchasing power comes from fake jobs created by the government, if there were no Oil &amp; Gas these fake jobs would not exist.

Should I still substract this component from the total GDP?

Is my reasoning correct?

NB: All data come from this website (and I'm not sure if I picked up the right values):
If I interpret your question correctly, you're asking what percentage of Algerian national income is derived from oil and gas extraction. The answer appears to be 30% from the website. 

I think the problem is you're assuming that the 30% figure means something like '30% of private spending', and so you're trying to account for government spending as well.

The website says 30% of GDP comes from oil and gas, that means 30% of income in Algeria is derived from oil and gas. It should already include government spending, which is taxed from income. And government spending should already include the fake jobs you mention.