Black defendants facing trial in Houston – the death penalty capital of America – are more than three times as likely to face a possible death sentence than whites, new academic research has revealed.

The study, by a criminologist at the University of Maryland, exposes the extent of racial discrimination inherent in the administering of capital punishment in Harris County, the ground zero of the death penalty in the US. The county, which incorporates Houston, Texas's largest city, has carried out 116 executions in the modern era – more than any entire state in the union apart from Texas itself.

Professor Raymond Paternoster of the university's institute of criminal justice and criminology was commissioned by defence lawyers acting in the case of Duane Buck, a death row prisoner from Houston whose 1995 death sentence is currently being reconsidered by the Texas courts.

Paternoster, whose report is based on the latest quantitative methods, looked at 504 cases involving adult defendants who had been indicted for capital murder in Harris County between 1992 and 1999 – the period during which Buck was charged for murdering his former girlfriend, Debra Gardner, and a man called Kenneth Butler. Paternoster whittled down that pool to 20 cases that most closely echoed that of Buck's own in terms of the factors involved in the crime that were likely to incur a death sentence.

He found that of the 21 men, including Buck, seven out of the 10 who were African American were sent by the Harris County district attorney for capital trial, compared with just one of the five white defendants.

"The probability that the district attorney will advance a case to a [death] penalty trial is more than three times as high when the defendant is African American than for white defendants," Paternoster writes. He adds: "The disparity by race of the defendant, moreover, cannot be attributed to observed case characteristics because these cases are those that were most comparable".

The huge disparity by race is only slightly ameliorated at the stage at which juries deliver their sentences: in Texas it is up to the jury to decide whether or not to send a convicted person to execution. Paternoster found that Harris County juries imposed death sentences on four of the seven African Americans put on capital trial, while also sentencing to death the only white defendant.

By imposing the death sentence on 100% of the white capital defendants in the sample while meting out the ultimate punishment to 57% of the black defendants, the juries to some extent corrected the glaring disparity of the initial charges. But the gulf remains: of the original group of 21 cases, the black defendants were more than twice as likely to be sentenced to death than their white counterparts.

The Paternoster report was filed on Wednesday with the Harris County district court as part of a habeus petition in Buck's case. Buck's lawyer, Christina Swarns of the NAACP legal defense fund, told the Guardian that it formed a pattern with past behaviour in Texas in the administering of the ultimate punishment. "Over generations there has never been a time in Texas when the death penalty did not yield evidence of racial discrimination. Any way you slice our new research, you find it."

The racial element of Buck's case is all the more prominent because his execution in September 2011 was halted by the US supreme court on grounds that his original sentence had been racially influenced. At his sentencing hearing in 1995, the jury heard testimony from a psychologist, Dr Walter Quijano, who told them that black people posed a greater risk to violent reoffending if released from jail than white prisoners.

The habeus petition chronicles the long and controversial history of the death penalty in Texas, particularly in Harris County. Though the county has a black population of 19%, African Americans represent almost 50% of the people detained in its jails, while 68% of the past 34 executions to emerge from the area involved black inmates.

The district attorney at the time of the Buck trial, Johnny Holmes, personally decided whether to seek the death penalty in every potential case. The petition states: "There is an abundance of evidence demonstrating that throughout Holmes' tenure, the Harris County district attorney's office excluded African Americans from jury service because of their race."

In 2001, Holmes was replaced as chief prosecutor in the county by Charles "Chuck" Rosenthal, whose tenure was no less contentious. In 2008, a batch of 1,500 emails from Rosenthal's official computer were released in a civil rights lawsuit in which racist "jokes" and slurs emerged relating particularly to African Americans. One such "joke" was that having Bill Clinton in the White House was akin to having a black president because he "smoked marijuana and receives a check from the government each month."

The Harris County district court is now considering whether or not to grant Buck a new sentencing hearing. A former assistant district attorney from the county, Linda Geffin, and Phyllis Taylor, an acquaintance of Buck's who was also shot by him in 1995 but survived, have called for his death penalty to be overturned.

Of the four black death row inmates in Paternoster's study, one has been executed, one died of cancer in prison, and a third, Jeffrey Demond, has his execution scheduled for 15 May. The last of the four is Duane Buck.