Lightly coat 3 cookie sheets with oil.
Combine sugar, syrup, and water in a large deep kettle. Bring to a boil stirring to make sure all the sugars melt and nothing sticks to the bottom. When the mixture reaches 260 degrees add butter, peanuts and continue stirring and cooking until the thermometer reaches 310 degrees.
Remove from heat and add vanilla and soda. Stir very quickly as the mixture becomes very foamy.
Immediately, if not sooner, pour the mixture out onto the cookie sheets.
After the brittle has hardened break into pieces. Put the brittle into large plastic bags so the shards don’t go flying all over the kitchen when breaking them up into smaller bite-sized pieces.
Store brittle in sealed jar, can or plastic bag to prevent from becoming very sticky.