The adsorption and reactions of the four butenes on porous Vycor glass at room temperature have been studied by infrared spectroscopy. Initial adsorption was rapid and was found to perturb the surface hydroxyl groups of the glass. In the case of then-butenes rapid isomerization took place at room temperature. In addition to this the adsorbate spectra showed the occurrence of a slower reaction which led to an increase in saturated C—H groupings. C8and higher compounds were shown to have formed; on outgassing at room temperature small amounts of cracking products were collected. The polymerization of isobutene was particularly rapid. Experiments at low coverage (θ ∼ 0.001–0.002) gave identical initial spectra for then-butenes. These were discussed in terms of possible models for butene adsorption. A reduction in the alumina and zirconia content of the glass by acid leaching resulted in decreased rates of isomerization and polymerization, suggesting that one or both of these oxides are at least partially responsible for the activity of the glass. A pure silica aerogel was almost completely inactive. Quantitative measurements of the spectra of several monoolefins in solution were made for comparison with the surface species, in particular with respect to their molar intensities of absorption.