Sulfonation of crude oils to produce petroleum sulfonates

A process for the secondary recovery of oil comprising in combination the steps of:

• (a) forming a micellar dispersion comprising hydrocarbon, water, and petroleum sulfonate produced by a process comprising contacting sulfur trioxide with a hydrocarbon selected from the group consisting of whole crude oil, topped crude oil, and mixtures thereof in a reaction zone at a temperature of about 26.6.degree. to about 121.degree. C., at a pressure of about 0.01 to about 150 atmospheres, and for a reaction time of about 0.001 to about 3600 seconds wherein about 5 to about 30 pounds of sulfur trioxide are contacted with each 100 pounds of hydrocarbon and wherein unreacted hydrocarbon after said contact with sulfur trioxide is removed by extracting the product mixture resulting from said contact of sulfur trioxide with said hydrocarbon with an extracton solvent selected from the group consisting of low molecular weight alcohol, ketone, ether, benzene, toluene, water or mixtures thereof and thereafter neutralizing the product with sodium hydroxide, potassium hydroxide or ammonia,
• (b) injecting at least a portion of said micellar dispersion into a petroleum-containing formation, and
• (c) displacing said micellar dispersion through said petroleum-containing formation to displace petroleum.