The methanol to olefins reaction has been studied in a small scale fluidized bed reactor over a phosphorus modified ZSM-5 catalyst. The product distribution was relatively insensitive to either feed rate or inlet gas composition. It was more sensitive to temperature with a significant increase in light olefins when the temperature was increased from 400 to 550 °C. A model based on the hydrocarbon pool mechanism is proposed in which olefins form through reversible reactions with a high molecular weight hydrocarbon species in catalyst pores and intersections. Agreement between the model and the product distribution of the olefinic species is good throughout the temperature interval investigated. Further experimental work is required to adequately characterize the paraffin and C₆₊ fractions.