In this paper, we demonstrate the first application of microfluidics to study diffusive transport in extra heavy oils, such as bitumen. A cross-channel glass microfluidic chip was used to measure the CO2 diffusion in Athabasca bitumen. The device was initially filled with CO2 at low pressure (< 1.0 bar). A plug of bitumen was injected into the central (50 mu m wide and 20 mu m deep) channel and, subsequently, exposed to high-pressure CO2 on both ends. One-dimensional oil swelling in response to CO2 diffusion was imaged over time. A simple mathematical approach was applied to calculate the diffusion coefficient based on the oil-swelling data. Measurement results are reported here at a range of pressures (1-5 MPa) and room temperature (21 degrees C). The measured diffusion coefficients in this range are on the order of 10(-10) m(2)/s, in good agreement with the relevant published data using conventional methods. In sharp contrast to conventional methods that require hours or days and similar to 0.5 L of sample, the method presented here requires similar to 10 min and a 1 nL plug of sample.