During the freeway drive, we ate some of the snacks but unknown to me at the time, my girlfriend moved the bag of snacks on top of the rear seat for better access. Later, when we climbed the twisty roads up the mountain, I remember hearing the sound of something falling over but didn't think much of it as I concentrated on driving. Once up the mountain and at the rental house, I started unloading the car. I noticed the bottle was on its side in the plastic bag I placed it in but it was nearly all empty! I inspected the bottle and saw that the cap was barely screwed on thus over 4qts had spilled onto the floor behind the driver seat. The rear floor mat was completely saturated in motor oil and the car's carpet underneath was the same. Pushing the carpet with a finger, I could see the oil had pooled.

I then realized it was the perfect storm of the bottle not being upright and the air pressure literally twisting the cap loose as I climbed from nearly sea level to over 5000ft since filling the oil. What a waste of $35 and an even bigger headache with the mess. I then researched methods of dealing with spilled oil inside a car and noted most recommended first absorbing the oil as much as possible with things like cat litter. I then went to a store and bought clay cat litter and poured it on the carpet before replacing the floor mat and pouring the rest of the litter on top. I kept it like that for about 24 hours until I got home the next day. The litter did absorb the excess pooling oil but wasn't going to do much about the saturation in the fabric of the carpet or floor mat. I've since removed the floor mat and soaked it in warm water with Dawn Ultra dish soap in a bucket over night. The water now looks like a grease tub. While the floor mat looks like it can be degreased and cleaned relatively easily with Dawn and then a dedicated degreaser, I'm a bit worried about the carpet of the car. I'm placing packing paper on there to absorb oil until I have more time to degrease and clean it. Depending on how things go with the floor mat with the products I'm using, I'll determine a plan of attack for the carpet.
Thankfully, the Pennzoil Platinum doesn't really have an odor. Didn't smell the oil at all when it leaked and saturated the carpet. Maybe it's because it's made from natural gas rather than crude oil. It's been odorless even in temperatures here ranging from 90 to 100 F this past weekend.