Abstract: A method of operating a spark ignition internal combustion engine with unleaded gasoline is disclosed wherein methylcyclopentadienyl manganese tricarbonyl (MMT) is used as a primary antiknock compound and from about 5 to about 60 moles of benzoylacetone or methyl benzoylacetone per mole of manganese is used as a co-antiknock compound. These co-antiknock compounds are particularly suitable because they do not react with wet rusted steel in gasoline distribution systems, nor with terneplate surface coatings in automobile fuel storage tanks.

Abstract: The reduction of octane requirement in a spark-ignited, internal combustion engine is achieved by introducing, with the combustion intake charge, a fuel and/or lubricant composition containing an octane requirement reduction amount of a substituted urea compound represented by the formula: ##STR1## in which X is an oxygen or sulfur atom, R.sub.1 and R.sub.3 are hydrocarbyl radicals having from 1 to 3 carbon atoms, and R.sub.2 is selected from the group consisting of ##STR2## Particularly useful as ORR agents are: (a) 4-[N-(2,4-xylyl) carbamoyl] morpholine;(b) 1-[N-(2,4-xylyl) carbamoyl] piperidine; and(c) 1-(2-pyridyl)-3-(3,4-xylyl)-2-thiourea.

Abstract: The reduction of octane requirement in a spark-ignited, internal combustion engine is achieved by introducing, with the combustion intake gasoline charge, a fuel and/or lubricant composition containing an effective octane requirement reduction (ORR) amount of a compound which is both highly polar and soluble in hydrocarbons and yet relatively insoluble in water and which is represented by the formula: ##STR1## in which X has a value from one to four, Y has a value from zero to three, and R is hydrogen or a hydrocarbyl radical having from one to three carbon atoms.

Abstract: The reduction of octane requirement in a spark ignition, internal combustion engine is achieved by introducing with the combustion intake charge a fuel and/or lubricant composition containing an octane requirement reduction amount of a compound represented by the formula: ##STR1## where R, R' and R" are hydrocarbyl groups having from 1 to 3 carbon atoms.