Approximately 70 M supergiants have been searched for Type I OH emission. OH was detected toward six stars but it is probably not associated with the stars in most cases. The results of this survey, combined with earlier searches for Type II OH supergiants, indicate that the OH luminosities are less for Type I supergiants than for Type II supergiants. There is also a trend for the OH luminosity to increase with the infrared color index. Similar effects have been noted for OH Miras, though these stars generally have smaller OH luminosities and color indexes. The results are consistent with OH supergiants having thicker dust envelopes than most OH Miras.