I would very strongly encourage you to watch the History Channel series 'The Men Who Built America', if you have the time. A great deal of the series is based around exactly this.
Both industries, in the US, got their big starts in Pennsylvania. In the case of oil, I believe it was while digging for salt by a man who's last name was Drake. Both industries were very focused around the railroad, which was the life blood of the US at the time. At first, there were many small operations, but men like Rockefeller did a lot of backroom deals, threatening, and outright killing to seize up as much of the industry as possible.
The major pro... money.
The major con... human dignity. The men who ran these industries were ruthless, and known for literally having people killed who stood in their way. Employees were treated like garbage, and efforts to unionize usually led to someone being murdered to death. Not to mention generations of negative health effects.