Which is almost absent in crude petroleum?

In petroleum refinery engineering, mercaptans are almost absent in crude petroleum (Option B).

Mercaptans, also known as thiols, are sulfur-containing organic compounds with the general formula R-SH, where R represents an organic group. While mercaptans can be present in refined petroleum products as contaminants, they are typically absent or present in very low concentrations in crude petroleum.

Therefore, the correct option is Option B: Mercaptans.