Subject Region
United States
262
Middle East
63
China
38
Saudi Arabia
37
Mexico
35
Nigeria
26
Russia (Federation)
26
Venezuela
26
Alaska
22
Canada
22
Iraq
22
Great Britain
21
Arab countries
19
Texas
19
Africa
18
Ecuador
18
Alberta
17
Persian Gulf Region
16
Iran
15
Pennsylvania
15
Soviet Union
14
Niger River Delta
13
Azerbaijan
12
Developing countries
12
United Arab Emirates
12
India
10
California
8
Caspian Sea Region
8
Japan
8
Persian Gulf States
8
Amazon River Region
7
Louisiana
7
Arctic National Wildlife Refuge
6
Argentina
6
Asia, Central
5
Europe, Eastern
5
Kuwait
5
Niger River Delta (Nigeria)
5
Ontario
5
Russia
5
South Africa
5
Africa, Central
4
Angola
4
Arctic regions
4
Bolivia
4
Brazil
4
Daqing (Heilongjiang Sheng)
4
Latin America
4
Libya
4
North Dakota
4
more ...