Workers' propensity to migrate to another local labor market varies a lot by occupation. We use the model developed by ? to quantify the impact of mobility costs and search frictions on this mobility gap. We estimate the model on a matched employer-employee panel dataset describing labor market transitions within and between the 30 largest French cities for two groups at both ends of the occupational spectrum and find that: (i) mobility costs are very comparable in the two groups, so they are three times higher for blue-collar workers relative to their respective expected income; (ii) Depending on employment status, spatial frictions are between 1.5 and 3.5 times higher for blue-collar workers; (iii) Moving subsidies have little (and possibly negative) impact on the mobility gap, contrary to policies targeting spatial frictions.