The different jackets represent which company the Locals (traders) deal for. The Oil Market, International Petroleum Exchange (IPE), is the largest floor based trading system in the UK. The shouting is to communicate prices, buying or selling, the type and month of stock you wish to buy to locals from other companies. As you mentioned, its incredibly noisy due to the shouting and prices e.t.c could be misheard. Therefore a second method to 'confirm' prices, months are needed. This is done using your fingers. All locals/traders have to learn this and take an exam before they are allowed into the 'pit'. Its very tricky to learn and decipher due to the speed thats used hence all the arm waving. I'm sure if you google this, you'll be able to find out the different 'finger denominations'. There's often long periods of the day when very little is going on and raised voices aren't used. The reason they all go mad at once can be due to many things i.e intrest rates announcments, non-farm payroll figures released, un/employment figures in the US, terrorist attacks, demand for particular stock e.t.c I'm guessing if it was a live feed on the news article you saw it would have been around about 2pm, which is when the American Energy Market opens. Generally though, the majority are ' wide boys' who like the sound of their own voices and feel that by shouting it somehow places them above everybody else.