Tornado Statistics

Tornado Statistics by year - The National Numbers
Source: http://www.spc.noaa.gov/climo/torn/monthlytornstats.html

Top 10 years for tornadoes in Oklahoma
Source: http://www.srh.noaa.gov/oun/?n=tornadodata-ok-monthlyannual

Ranking Year Tornadoes Ranking Year Tornadoes
1 1999 145 6 1998 83
2 1957 107 7 1961 82
3 1982 101 8 1995 79
4 1960 98 9 2003 78
5 1983 92 10 1955
2008
77
77

Oklahoma Tornadoes in 1999

The most tornadoes were reported in 1999.  Here's the stats for deaths and injuries by severity of the tornado.  It's based on the Fujita scale.

Scale Tornadoes Deaths Injuries
F0 80 0 0
F1 40 0 1
F2 13 1 17
F3 9 2 45
F4 2 3 37
F5 1 36 583
Total 145 42 683

The May 3rd, 1999 tornado outbreak

During a two day period in 1999, May 3rd and May 4th, Oklahoma storms produced 71 tornadoes.   The F5 tornado that touched down near Oklahoma City on May 3rd stayed on the ground for over an hour.  At the conclusion of the outbreak on May 4th, 40 people were dead and 672 were injured.  Classified the 6th deadliest tornado in U.S. history and the most expensive, causing over $1.1 billon in property damage.