Petroleum crude oil is called as sweet when the sulfur content is less than 0.5%. Sweet oil is used for production of gasoline, kerosene and diesel. Its called sweet because it is having a pleasant smell and mildly sweet taste due to low level of sulfur.
Sour crude oil is having sulfur content greater than 0.5% and is toxic as it evolves hydrogen sulphide.
Crude oil sweet and sour is listed in IMDG Code as below
UN 1267 PETROLEUM CRUDE OIL
Un 3494 PETROLEUM SOUR CRUDE OIL, FLAMMABLE, TOXIC
IMDG Code Compliance Centre 
Sir, this is a new knowledge to me. Thank for the post.
Thanks Radhika
Regards/Shashi