You have to look over the whole map. An oil refinery that is auto producing could be faster. What determines output is, a willing partner to receive the goods. For instance..
Steel Mill – Iron Mine-Coal Mine. This chain can produce up to 400 Tons of goods. Depending on how may cities it is shipping to determines the output. For instance… City A needs 45 Goods, City B needs 37 Goods, City C needs 55 goods. So, you have those 3 cities hooked to steel mill. They can take up 137 Goods. That means the max output of that factory will be 200, until you have more outlets for the goods.
Now, as the game progress’s the auto chains can interfere with your shipping. If the roads can get the freight there faster. I suspect this is your issue, look at all of the auto chains.