Oil soluble dispersants suitable for use in fuels and lubricants

An oil-soluble lubricating oil dispersant formed by reacting

• (a) at least one oil-soluble lubricating oil dispersant selected from (i) substituted succinimide dispersant in which the substituent is derived from a C.sub.2 to C.sub.5 monoolefin polymer having a number average molecular weight within the range of 700 to 3000, said succinimide dispersant having at least one acylatable primary or secondary amino group, (ii) substituted succinic esteramide dispersant in which the substituent is derived from a C.sub.2 to C.sub.5 monoolefin polymer having a number average molecular weight within the range of 700 to 3000, said succinic esteramide dispersant having at least one acylatable primary or secondary amino group, and/or at least one acylatable hydroxyl group, and (iii) Mannich condensation product formed by condensing long chain hydrocarbyl substituted hydroxyaromatic compound with aldehyde and polyamine, said, Mannich condensation product containing at least one acylatable primary or secondary amino group, wherein said long chain hydrocarbyl substituent has 50 to 300 carbon atoms and is dived from a polymer of a C.sub.2 to C.sub.5 mono-.alpha.-olefin, with
• (b) at least one modified polymer of isobutene of the formula ##STR32## where R.sup.1 is an olefinically unsaturated divalent radical, R.sup.2 is one of the divalent radicals. ##STR33## and m an n are each at least 1.