The barrel is a unit of volume used in the oil industry with the symbol bbl.
Oil is more commonly expressed in terms of cubic metres (m³) but in the US and in the economic world (mainly because such a large percentage of the world's oil is shipped to the US) as barrels.
The measurement of the barrel originated in the US at the first oil well in Pennsylvania. There were so many variants of barrel size (including those used for wine and other goods) that the distrust became so prevalent a central and standard barrel size was created. This was finally established in 1872 as 42 US gallons.
The teaspoon is a unit of volume in the US customary system and uses the symbol Tsp.
In the kitchen, the teaspoon is the smaller of the commonly used spoons served at the table and represents 1/6 US fluid ounce, 1/48 US cup or, expressed in SI / metric format; 4.92892159375 ml.
A teaspoon is generally considered a cooking measure but is also used in the administration of medicine when in solution form; 5 ml or multiples thereof is the standard amount of liquid medicine across the world.