Region
United States
423
California
245
Texas
173
Kansas
132
Wyoming
127
Oklahoma
102
Pennsylvania
101
China
98
Middle East
82
West Virginia
74
Canada
67
Illinois
66
Alaska
65
Colorado
63
Russia (Federation)
61
New Mexico
58
Louisiana
56
Alberta
55
Utah
54
Europe
49
Soviet Union
49
North Dakota
46
Kentucky
44
Kern County
44
Montana
43
Former Soviet republics
38
Mexico, Gulf of
38
Nebraska
37
Ohio
37
Africa
35
North Sea
35
Israel
31
Mexico
31
Australia
30
Nigeria
30
Iran
29
Michigan
28
Indiana
26
Iraq
26
British Columbia
25
Japan
24
Asia
22
Kern County (Calif.)
22
Saskatchewan
22
Arkansas
21
Asia, Central
21
Caspian Sea Region
21
South America
21
Arabian Peninsula
20
New York (State)
20
more ...