The inside of my Suzuki Alto smells like exhaust/gas/oil. The smells seem to be coming through the ventilation system when the fan is blowing.
What could cause these conditions?
Stop the car, open the bonnet and check that you don't have an oil leak. You may find an area of the engine or underbonnet is covered with black oil. Also check under the car for any signs of oil leaking.
If no oil leak, check all hoses are tightly located where they should be. A loose breather hose could cause this.