Gasoline pyrolysis, isolation of C-4 fraction, and extn. distn. continue to account for 90% of world's butadiene production. Dehydrogenation of n-butane and butylenes is energy- and cost-too-intensive. For decades there has been no breakthrough, but only modifications and refinements in butadiene processes. With the butadiene production placed in a broader-construed complex of the C-4 fraction market, the needs can be more flexibly met and the diffs. between the demand for ethylene/propylene and that for butadiene minimized.