How to stealth Big Oil : Day One?

I've been trying to stealth it with some friends but we're failing it so bad :(

Does anyone have some tips about this mission ?

Here is a guide on how to complete Big Oil: Day One without setting off any alarms. Like stealthing any other mission in Payday 2, the key ingredients are patience and precision. If you get sloppy for even a second during this mission (both day one and day two) you will set off an alarm.

Mission Objective

You arrive at a house controlled by the Overkill biker gang, the house contains information relating to the development of a fusion reactor. Get into the house, get the intelligence, and get out again.

The Intelligence

The bulk of the intelligence you'll find will be on tables and countertops throughout the house but the mission objective is to drill a titan safe to get a piece of paper out of it. The other pieces of intel available for collection in this mission are as follows;

• Airplane keys (allows fast escape from day 2)
• Blueprints to the house (not really useful since the house layout is pretty consistent)
• Picture of the security guards (no real use at all)
• Shutter codes

In the event you find the safe before you've killed everybody it can be drilled if it's out of sight with a quiet or silent drill, reducing the amount of time in the mission. If you find yourself in a situation where the safe is on the ground floor, and you've taken out all of the bikers in the level that are roaming, you can also complete the level without killing everybody if you're willing to skip out on other pieces of intel.

The Plan

The bikers know you're coming and are on the lookout. There are a variety of randomisations that can change how this plays out. In addition, they've got a very vigilant member of their gang on security detail watching the cameras. This means:

• Breaking any cameras will set off the alarms
• Getting spotted will set off the alarms
• There is a chance that the fence around the house is electrified
• There is a chance that the area around the house is littered with land mines

The plan, in essence, is simple:

• Enter the property
• Navigate your way to the house without getting spotted by the lookouts or the cameras
• Take out all of the guards one by one without any of the kills being spotted
• Collect all of the intelligence located around the house
• Drill the safe containing the address of the scientist making the reactor
• Leave the house

Nice and simple - it gets better too, while there are a large number of bikers around the house, there are no pagers to answer. Killing them is simply a case of pulling a trigger and bagging the bodies. There is a locked room below the house full of ATMs that is ideal for storing the bodies and the garage below the house is a pretty ideal kill room.

You'll want to clear as many guards as possible by waiting for them to come down to the garage before you try and breach the house. Getting spotted is an alarm within a second or so, meaning if you get caught between a pair of bikers, or another biker spots one of your kills, the "stealth" section of the mission is over.

As mentioned, my preferred method of doing this is using the garage as a kill room, and then clearing the side room (the room below the upstairs balcony) and then the main room with all of the entrances to the building in it. There is occasionally a biker at the top of the stairs and there are occasionally bikers walking outside as well and you will want to be careful of these in particular, since they're normally in view of other bikers, and if they spot something it will alert multiple others all over the house, preventing you from keeping the situation under control.

Here is a video on YouTube that demonstrates day one of Big Oil being stealthed: