As Oakland's crime rate has skyrocketed, police overtime costs have soared way over budget, city documents show.

Last year, Oakland spent $21.8 million for police overtime and was over budget by $6.6 million. In contrast to last year, OPD overtime cost for the city was $15.2 million - under budget by $2.8 million.

Meanwhile, police labor cost for the city has gone down - from $151 million in 2011 to $144 million in 2012.

Budget information on the city's police budget was provided to Oakland Local as a result of a California Open Records request.

Crime in Oakland has risen dramatically - spiking 20 percent from the previous year. The city saw 135 people murdered in 2012.

Police brass say that overtime is the result of not having enough number of sworn officers as the city has experienced a rise in crime. Current sworn staffing levels have been reduced from 830 in January 2009 to 640 in 2012.

Police overtime work is happening in nearly every department. In a recent report to City Council, Oakland Police Chief Howard Jordan said that with low officer numbers and high service calls, OPD has no choice but to use overtime to fight crime. OPD officers are now required to work mandatory overtime.

"Without new officers to backfill for vacancies, OPD must use overtime to backfill, collapse units into patrol, or leave the position (beat) vacant," Jordan wrote.

Officials said that they've tried to minimize overtime. Efforts to reduce overtime include plans to bring in temporary assistance for the California Highway Patrol. The city also has plans to receive assistance from the Alameda County Sheriff's office.

OPD did not respond to calls for comment about overtime for this story.