Oil-soluble polysubstituted long - chain alkanes, suitable for use as oil additives, contain attached to a plurality of the carbon atoms of the alkane chain a plurality of hydrolysis-resistant oil-solubilizing radicals, each containing an uninterrupted hydrocarbon group of at least 8 carbon atoms, a plurality of alkoxycarbonyl radicals and a plurality of N-substituted carbamyl or thiocarbamyl radicals wherein at least one of the substituents to the N-atom is a polar organic radical attached to the N-atom by an N-C linkage, the ratio of the average number of alkoxycarbonyl plus N-substituted carbamyl radicals to the number of hydrolysis-resistant oil-solubilizing radicals is between 4 to 1 and 1.1 to 1 and at least 10 per cent but not more than 90 per cent of the total alkoxycarbonyl plus N-substituted carbamyl radicals are N-substituted carbamyl radicals. The polysubstituted alkanes, preferably of molecular weight between 2,000 and 150,000, are prepared by copolymerizing (1) an ethylenically unsaturated monomer having a single terminal ethylenic group and an uninterrupted chain of at least 10 carbon atoms; (2) an ester of an ethylenically unsaturated carboxylic acid and a lower alkanol; and (3) an N-substituted amide of an unsaturated carboxylic acid wherein at least one of the substituents to the N-atom is a polar organic radical attached to the N-atom by an N-C linkage. The monomer (1) is preferably a normal or branched chain a -olefine containing from 16 to 30 carbon atoms, e.g. n-hexadecene-1, n-octadecene-1, n-tricosene-1, and n-octacosene-1, which may be obtained by cracking paraffin waxes, or a vinyl ester, ether, or ketone and numbers of these compounds are listed. The esters (2) may be derived from mono- or poly-carboxylic acids, and esters of acrylic, methacrylic, chloroacrylic, a -isopropylacrylic, a -amylacrylic, a -cyclohexylacrylic, a - hexylacrylic, maleic, chloromaleic, hexylmaleic, itaconic, glutaconic, aconitric, 2-pentenedioic, and 3-octenedioic acids are listed. The amides (3) may be derived from the unsaturated acids mentioned under (2) and, attached to the nitrogen atom of the amide group, they may have polar groups which contain a non-metallic negative atom from Group V or VI of the Periodic Table. Examples of such amides are N-butanol, N-hexanol, and N - (3 - aminopropyl) - methacrylamide; N - (ethanol), N - (5 - carboxy - hexyl), N - morpholinoethyl, N - (dimethyl amino ethyl), N-(dimethylamino propyl), N-(6-mercapto-octyl), N - (6,6 - dihydroxyethyloctyl), N - (6 - cyanohexyl), N - (6 - hydroxyoctyl) - a - octyl and N - (6 - thiocyano - octyl) acrylamide; N,N-di - (6 - hydroxyoctyl) maleamide; N,N - di-(dimethylaminoethyl) itaconamide; and N,N-di - (mercaptobutyl) and N - (4 - hydroxyhexyl) butyl aconitamide. The monomers (2) and (3) may be reacted together first and the product e.g. N-(b -dimethylaminoethyl) acrylamide copolymerized with the alkene, e.g. n-octadecne-1. Additional polar groups may be introduced by conducting the polymerization in the presence of other polymerizable vinyl monomers, e.g. vinyl acetate, and such groups may be converted to hydroxyl groups by hydrolysis of the resulting copolymer. In an alternative and preferred method of preparation, the monomers (1) and (2) are first copolymerized and then treated with a primary or secondary amine, the N-atom of which bears at least one polar organic radical attached to the N-atom by an N-C linkage. Amines are listed and a sufficient quantity is used to convert at least 10 per cent but not more than 90 per cent of the alkoxycarbonyl groups into N-substituted carbamyl radicals. In examples: (1) a copolymer of octadecene-1 and methyl acrylate is prepared and reacted; (2) with N,N-dimethylaminopropyleneamine; (3) with N,N-diethylaminopropyleneamine; or (4) with monoethanolamine; (5) a copolymer of vinyl stearate and methyl acrylate is prepared and reacted with N,N-dibutylpropane-1,3-diamine or aminoethyl morpholine; (6) a copolymer of n-hexadecene-1 and methyl methacrylate is reacted with 4-aminobutyl mercaptan, 1-cyano-5-aminopentane or 1-thio-5-aminopentane; (7) a copolymer of octadecene-1 and methyl acrylate is reacted with 4-amino-butyraldehyde; (8) 4-aminopentanamide; (9) 4-aminopentanoic acid or (10) N-hydroxyethylethylenediamine; and (11) a methyl a -octadecyl acrylatevinyl acetate copolymer is reacted with N-aminoethylmorpholine. The polysubstituted alkanes may be used in oil compositions in minor amounts, e.g. from 0.001 to 10 per cent as sludge preventives, detergents, antiwear agents and antioxidants. They may be used in natural lubricants, e.g. hydrocarbon oils, alone or blended with castor or lard oil, or in synthetic lubricants such as polymerized olefines, copolymers of alkylene glycols and oxides, organic esters of polybasic organic and inorganic acids, e.g. di-(2-ethylhexyl sebacate), dioctyl phthalate and trioctyl phosphate, polymeric tetrahydrofuran and polyalkyl silicone polymers, e.g. dimethyl silicone polymer. They may also be used in greases, fuels (e.g. gasoline, gas oil or burner fuel oil), and slushing, industrial, metal working, drawing, quenching, and textile oils. Other conventional additives such as antioxidants, detergents, pour point depressants, viscosity index improvers, blooming agents, corrosion inhibitors, oiliness agents and solubilizers may also be present. Examples of such conventional additives are given. Specification 714,178 and U.S.A. 2,639,227 are referred to.ALSO:Oil-soluble polysubstituted long chain alkanes, suitable for use as hydrocarbon oil additives, contain attached to a plurality of the carbon atoms of the alkane chain a plurality of hydrolysis-resistant oil solubilizing radicals, each containing an uninterrupted hydrocarbon group of at least 8 carbon atoms, a plurality of alkoxycarbonyl radicals and a plurality of N-substituted carbamyl or thiocarbamyl radicals wherein at least one of the substituents to the N-atom is a polar organic radical attached to the N-atom by an N-C linkage, and the ratio of the average number of alkoxycarbonyl plus N-substituted carbamyl radicals to the number of hydrolysis-resistant oil solubilizing radicals is between 4 to 1 and 1.1 to 1 and at least 10 per cent but not more than 90 per cent of the total alkoxycarbonyl plus N-substituted carbamyl radicals being N-substituted carbamyl radicals. The alkanes preferably of molecular weight between 2,000 and 150,000 are prepared by copolymerizing (1) an ethylenically unsaturated monomer having a single terminal ethylenic group and an uninterrupted chain of at least 10 carbon atoms; (2) an ester of an ethylenically unsaturated carboxylic acid and a lower alkanol; and (3) an N-substituted amide of an unsaturated carboxylic acid wherein at least one of the substituents to the N-atom is a polar organic radical attached to the N-atom by an N-C linkage. The monomer (1) is preferably a normal or branched chain a -olefine containing from 16 to 30 carbon atoms, e.g. n-hexadecene-1, n-octadecene-1, n-tricosene-1, and n-octacosene-1, which may be obtained by cracking paraffin waxes, or a vinyl ester, ether, or ketone and numbers of these compounds are listed. The esters (2) may be derived from mono- or polycarboxylic acids, and esters of acrylic, methacrylic, chloro-, a -isopropyl, a -amyl, a -cyclohexyl, a -hexylacrylic, maleic, chloromaleic, hexylmaleic, itaconic, glutaconic, aconitic, 2-pentandioic, 3-octenedioic acids are listed. The amides (3) may be derived from the unsaturated acids in (2) with functional groups which contain a non-metallic negative atom from Group V or VI of the Periodic Table, and examples are N-butanol, N-hexanol, and N-(3-aminopropyl)methacrylamide, N-(ethanol), N-(5-carboxyl-hexyl), N-morpholinoethyl, N-(dimethylaminoethyl), N-dimethylaminopropyl), N-(6-mercaptooctyl), N-(6,6-dihydroxyethyloctyl), N-(6-cyanohexyl), N-(6-hydroxyoctyl)-a -octyl and N-(6-thiocyanooctyl) acrylamides, N,N - di - (6 - hydroxyoctyl) maleamide, N,N-di-(dimethylaminoethyl) itaconamides, and N,N-di-(mercaptobutyl) and N-(4-hydroxyhexyl) butyl aconitamides. The reactants (2) and (3) may be copolymerized first and the product, e.g. N-(b -dimethylaminoethyl) acrylamide reacted with the alkene, e.g. n-octadecene-1, and additional polar groups incorporating other polymerizable monomers, e.g. vinyl acetate may be present and may be hydrolysed in the resulting copolymer. In an alternative and preferred method of preparation, the monomers (1) and (2) are first copolymerized and then treated with a primary or secondary amine, the N-atom of which bears at least one polar organic radical attached to the N-atom by an N-C linkage. The concentration of monomers is controlled so that the copolymers contain between 4 and 1.1, alkoxycarbonyl groups per unit derived from (1) by shortstopping the reaction or by adding monomers to maintain the concentration constant. The copolymers may be prepared in bulk, solution, or aqueous emulsion or suspension systems with catalysts such as hydrogen, benzoyl, lauroyl, and di-(t-butyl) peroxides, t-butyl hydroperoxides, 2,2-bis-(t-butyl peroxy) butane, t-butyl perlargonate sodium or potassium persulphates, percarbonate and peracetic acid, at an elevated temperature, under atmospheric, reduced or elevated pressures, and if desired in the absence of air. Chain transfer agents such as alcohols, aldehydes, ketones, ethers, halogenated hydrocarbons, alcohols, aldehydes, ethers or organic acids, acid halides, esters of inorganic esters, and amines, cyanogen and nitro compounds, sulphur halides, benzene sulphonyl chloride, mercaptans and related organic sulphur compounds may be present. Amines are listed and a sufficient quantity is used to convert at least 10 per cent but not more than 90 per cent of the alkoxycarbonyl groups into N-substituted carbamyl radicals. The components are mixed alone, or in a mutual solv