  Our experiments on viscous fingering of air into oil contained between
closely spaced plates reveal two selection rules for the fjords of oil that
separate fingers of air. (Fjords are the building blocks of solutions of the
zero-surface-tension Laplacian growth equation.) Experiments in rectangular and
circular geometries yield fjords with base widths 1/2 lambda_c, where lambda_c
is the most unstable wavelength from a linear stability analysis. Further,
fjords open at an angle of 8.0 degrees plus or minus 1.0 degree. These
selection rules hold for a wide range of pumping rates and fjord lengths,
widths, and directions.
