NOVELTY - As an efficiency improver in a motor fuel composition, at least partially esterified and/or etherified, straight, branched or cyclic, di- or polyhydroxy 2-12C hydrocarbon derivative or its ketal or acetal, is used.    USE - As an efficiency improver additive in a motor fuel composition, as a soot particles enlarging agent, and/or a soot emission reducing agent; as an octane number improving agent; where the motor fuel composition is a diesel fuel composition, or a gasoline, a jet fuel, or a gasoline/ethanol mixture (all claimed).    ADVANTAGE - The triglyceride derived additives provide remarkable efficiency improvement, when added to different diesel formulations; the additives are required in small amounts; and provide reduced soot generation, where soot particles are larger than those produced in the absence of the additives.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (i) conversion of a 10-30C fatty acid triglyceride into 1-5C alkyl esters of 10-30C fatty acids containing phase and 1-5C alkyl ethers of glycerol containing fraction, where a fatty acid triglyceride has a formula (CH2-OR1)-(CH2-OR2)-(CH2-OR3) (I), is reacted with a lower alkanol, preferably a 1-5C alkanol (more preferably methanol), in the presence of a catalyst (preferably a basic catalyst, especially KOH), to obtain a 2-phase mixture, consisting, on the one hand, of a glycerol and lye containing phase; and on the other hand, a 1-5C alkyl esters of 10-30C fatty acids containing phase; the 2 phases are separated and, if desired, dried; the catalyst is neutralized, and an acid catalyst is added; and the glycerol containing phase is, in the presence of the acid catalyst (preferably an acid ion exchanger comprising Amberlyst-15 (RTM: acid ion exchanger)), reacted with 1-5C alkyl ether (preferably methyl tert-butyl ether (MTBE), or methyl tert-amyl ether (MTAE)), to obtain an alkyl ether containing fraction (preferably a glyceryl tert-butyl ether (GTBE) or glyceryl tert-amyl ether (GTAE) containing fraction); the thus obtained fraction is, if desired, purified according to a known process; the fraction is, if desired, combined with the 1-5C fatty acid esters containing phase to obtain a mixture of 1-5C alkyl esters of 10-30C fatty acids and glyceryl 1-5C alkyl ethers; (ii) preparation of a compatability improving agent for an ethanol/gasoline motor fuel composition, where a straight, branched or cyclic di- or polyhydroxy 2-12C hydrocarbon derivative is partially etherified with a 1-5C alkyl ether, in the presence of a catalyst, to obtain a composition of 1-5C alkyl ethers of di- or polyhydroxy 2-12C hydrocarbon derivative, having free OH functionalities; and (iii) preparation (M1) of an efficiency improving and soot particles enlarging agent for a diesel motor fuel composition involving either: (a) transesterification reaction of a straight, branched or cyclic, di- or polyhydroxy 2-12C hydrocarbon derivative with a stoichiometric excess of a lower alkyl ester of a lower alkyl carboxylic acid (preferably a 1-5C alkyl ester of 1-5C carboxylic acid), in the presence of a catalyst, to obtain a mixture of lower alkyl esters of the di- or polyhydroxy 2-12C hydrocarbon derivative and lower alkanol (preferably a mixture of 1-5C alkyl esters of di- or polyhydroxy 2-12C hydrocarbon derivative and 1-5C alkanols); or (b) interesterification reaction of a fatty acid triglyceride having formula (I) with a stoichiometric excess of a lower alkyl ester of a lower carboxylic acid (preferably a 1-5C alkyl ester of 1-5C carboxylic acid), in the presence of a catalyst, to obtain the agent as a mixture of glyceryl carboxylic esters (preferably glyceryl acetyl esters) and 1-5C alkyl esters of 10-30C fatty acids (preferably methyl or ethyl esters of 10-30C fatty acids).    R1-R3=straight or branched, 10-30C alkyl carboxylic group.