Stefan is a Distinguished Scientist at Alberta Innovates – Technology Futures in Alberta, Canada. For the last two decades Stefan has focused his research interest and efforts on the potential for, and risks of CO₂ storage in geological media as a mitigation strategy for reducing greenhouse gas emissions into the atmosphere. Between 2002 and 2005 Stefan contributed as a Lead Author to the IPCC Special Report on CO₂ Capture and Storage, in which capacity he is co-sharing in the 2007 Nobel Peace Prize awarded to IPCC.

Between 2005 and 2007 Stefan represented Alberta on the Interstate Oil and Gas Compact Commission Task Force on CO₂ Storage. In 2007 Stefan served on the Technical Working Group of the Canada-Alberta EcoEnergy Task Force on Carbon Capture and Storage. Between 2009 and 2012 Stefan has contributed to the Canadian Standards Association standard on Geological Storage of Carbon Dioxide.

Since 2004 Stefan represents Canada on the Technical Group of the Carbon Sequestration Leadership Forum (CSLF), where he chaired the CSLF Task Force on CO₂ Storage Capacity Estimation and the Task Force on Technological Challenges in the Transition from CO₂-EOR to CO₂ Storage. In 2011 and 2012 Stefan co-chaired the Expert Panel that advised the Government of Alberta on Regulatory Framework Assessment for CO₂ Capture and Storage.

Stefan is Associate Editor of the International Journal of Greenhouse Gas Control. He has published 182 papers in journals and conference proceedings, made more than 300 presentations and wrote 104 professional reports, of which more than half are on the subject of CO₂ sequestration in geological media as a climate-change mitigation strategy.