<PICT:0719003/III/1> <PICT:0719003/III/2> <PICT:0719003/III/3> Crude petroleum is refined by first distilling to give a plurality of lighter fractions and a residue of reduced crude; one or more of the lighter fractions is then subjected to a conversion operation (e.g. cracking hydroforming), the reduced crude is passed to an intermediate point of a fractionating column and the vapours from the conversion reaction(s) and, if available, at least one of the lighter fractions as such are passed into the same column below the point of introduction of the reduced crude to strip it of volatiles. Various streams are taken from the column and may be taken to storage, or further refined or recycled to a previous conversion stage. In Figs. 1 and 1A crude oil from line 101 is heated in furnace 107 and passed to column 110. Bottoms from column 110 are passed by line 122 to the upperpart of the stripper section A of a fractionating tower 140. The overhead vapours from column 110 are heated in coil 117 disposed in a conversion reactor 130 and passed by line 116 to the base of section A of tower 140 Kerosine or diesel oil is taken off at 120 and heavy naphtha at 118, this fraction passing through a conventional hydroforming, thermal reforming or other conversion stage 130. Vapours from 130 are taken to the stripper section A of tower 140 by line 134. From tower 140 a gas oil stream is taken off by line 142 at the base of the rectifier section, partly returned by line 144 as reflux and partly taken off by line 146 to a cracking unit 150, which may be that described in Specification 716,242, the vapours from which are returned to the stripper section A by line 152. The bottoms from tower 140 may be quenched by being passed from draw-off line 147 through cooler 153 back to the tower by line 155. Bottoms product is taken off by line 194 via filter 190. From the rectifying section B of the tower 140, heating oil is taken off at 156, mostly returned to the top of section B via cooler 158 and line 162 as absorber lean oil, and the remainder stripped in 157 and taken to product by line 178 or as fluxing oil for the heavy residue via lines 183, 181 and 155, vapours returning to the column at 159. Above line 156 heating oil is condensed out of the vapours by cooled heating oil entering through line 168, while C5, C4, and C3 hydrocarbons with which the heating oil entering by 168 is saturated, are stripped by the ascending naphtha and gas product vapours. Such vapours are fractionated by reflux from line 176 and the fractionated vapours removed at 166 and compressed at 169. Naphtha is condensed at 172, stripped at 173 and the product removed at 170. Gas and light fractions from stripper 173 are led to the absorber portion of section B by line 177, residual gas from which all gasoline components have been absorbed passing off at 164. In modifications, (i) the bottom portion of section A may be operated at viscosity breaking conditions, e.g. 875-950 DEG F.; (ii) alternatively, or in addition the reduced crude may pass through a thermal or catalytic coking or viscosity breaking treatment before entering stripper section A; (iii) all or part of the bottoms may be subjected to a coking or viscosity breaking treatment at 182 the resulting vapours being passed from separator 184 to a middle portion of section A, heavy residium and coke passing to filter 190. The apparatus described with reference to Figs. 2 and 2A (not shown) as similar to that shown in Figs. 1 and 1A but differs in that the reforming stage 130 is replaced by a catalytic hydroforming stage to which may be fed, in addition to the heavy naphtha stream from column 110, a hydrocarbon stream of similar boiling range from tower 140; a certain proportion of gases from the hydroforming stage may be passed to later hydrogenation stages to improve the cracking characteristics of cracking recycle stock from tower 140 and the quality of product light gas oil recovered from tower 140. The liquid hydroformate may be blended without further treatment with finished gasoline from tower 140. In the arrangement of Fig. 4 residuum from crude column 110 is passed to stripper 435 and is there stripped by the effluent from hydroforming stage 130 fed with heavy naphtha from column 110 by line 128. Stripped reduced crude is then taken by line 441 to tower 140 where it is further stripped by cracked vapours from cracking stage 150. The overhead from stripper 435 is cooled at 447 and separated at 449, gas being returned to hydroforming stage 130, and liquid passed to fractionating section B of tower 140. Part or all liquid may however be passed to a separate fractionator 460. A gas oil may be recovered as bottoms from tower 460 and combined with gas oil in line 142 to be further treated as in Figs. 1 and 1A. Virgin naphtha from lines 116 and/or 118 is supplied to the bottom of tower 140 to assist in further stripping the stripped reduced crude from stripper 435. The Specification also describes (Fig. 3 not shown), a multistage hydroforming unit which may be used in the process of the invention.