2 cao ca oh 2 mgo mg oh 2 mgcl 2 bao baoh etc presently the calcium salts are preferred for use the resulting group ii a salts of polyalkenylthiophosphonic acid have the proposed structure str1 wherein x is a group ii a cation such as ca mg or ba r is the polyalkenyl moiety remaining after reaction of the alkenyl polymer with p 2 s 5 the molecular weight of the r moiety may be within the range of about 500 10 000 r is preferably a polyisobutenyl residue but polyethylene polypropylene polybutylene and polyamylene may also be used the antifoulant presently preferred for use has the structural formula str2 wherein r is the polyisobutenyl residue remaining after reaction of polyisobutene with p 2 s 5 calcium polyisobutenylthiophosphonate the molecular weight of r is around 750 2 000 the antifoulants are dispersed within the petroleum hydrocarbon or petrochemical within the range of about 0 5 10 000 ppm of antifoulant based upon one million parts petroleum hydrocarbon or petrochemical preferably the antifoulant is added in an amount of from about 1 1 000 ppm the invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustrative and not as restricting the scope of the invention in order to ascertain the antifoulant efficacy of.