| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 37 | 284 | 324 | |
| 2020 | R | 39 | 298 | 348 | |
| 2016 | R | 30 | 278 | 322 | |
| 2012 | R | 49 | 240 | 298 | |
| 2008 | R | 68 | 227 | 300 | |
| 2004 | R | 55 | 228 | 292 | |
| 2000 | R | 36 | 254 | 306 | |
| 1996 | R | 62 | 186 | 290 | |
| 1992 | R | 61 | 135 | 296 | |
| 1988 | R | 91 | 204 | 302 | |
| 1984 | R | 86 | 258 | 347 | |
| 1980 | R | 90 | 225 | 341 | |
| 1976 | R | 110 | 211 | 331 | |
| 1972 | R | 87 | 232 | 325 | |
| 1968 | R | 98 | 211 | 335 | |
| 1964 | D | 210 | 190 | 401 | |
| 1960 | R | 221 | 255 | 476 | |
| 1956 | R | 205 | 258 | 463 | |
| 1952 | R | 155 | 319 | 474 | |
| 1948 | D | 235 | 214 | 461 | |
| 1944 | R | 225 | 253 | 481 | |
| 1940 | D | 316 | 313 | 631 | |
| 1936 | D | 523 | 258 | 806 | |
| 1932 | D | 544 | 351 | 924 | |
| 1928 | R | 372 | 586 | 963 | |
| 1924 | — | — | — | — | |
| 1920 | — | — | — | — | |
| 1916 | — | — | — | — | |
| 1912 | — | — | — | — | |
| 1908 | — | — | — | — | |
| 1904 | — | — | — | — | |
| 1900 | — | — | — | — | |
| 1896 | — | — | — | — | |
| 1892 | — | — | — | — | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
With fewer than 500 residents spread across high-plains ranch land, Petroleum County consistently posts some of the most lopsided Republican margins in the nation — the 2024 gap of 76 points reflects both its demographic uniformity and extreme rural isolation.
The Democratic margin in Petroleum County peaked at thirty-three points in 1936. By 1968 the county had flipped, voting Republican for the first time in many years. The 2024 margin was seventy-six points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Petroleum County's median household income of $60,208 sits well below state and national norms, and 8% of residents live below the federal poverty line. The shift here is part of a broader realignment of working-class places across the country. The county's voting pattern over the last decade is most similar to that of Fergus County and Blanco County.