Large bulk matter search for fractional charge particles

We have carried out the largest search for stable particles with fractional electric charge, based on an oil drop method that incorporates a horizontal electric field and upward air flow. No evidence for such particles was found, giving a 95% confidence level upper limit of 1.17x10(-22) particles per nucleon on the abundance of fractional charge particles in silicone oil for 0.18eless than or equal toparallel toQ(residual)parallel toless than or equal to0.82e. Since this is the first use of this new method we describe the advantages and limitations of the method.