Breathing petroleum vapors can cause nervous system effects.
Very high exposure can cause coma and death.
Petroleum products that come in contact with the skin can cause irritation and some can be absorbed through the skin.
Chronic exposure to petroleum products can affect our blood and kidneys.
Gasoline contains benzene, a known human carcinogen.
Animals exposed to high levels of some petroleum products can develop liver and kidney tumors.  
People in the petroleum refining industry have an increased risk of skin cancer and leukemia.