I wondered, which uses more oil to get manufactured and delivered to me - a glass bottle of brown sauce(*), or the same volume of sauce in a squeezy plastic bottle?
The plastic bottle is made from oil, but it's lighter so takes fuel to transport to me. It's also thinner, so I assume that you can fit more in the same vehicle, which will also increase the efficiency.
I'm assuming that the energy used to manufacture both wasn't oil. If it is (or if you take total fuel costs instead), I'm not sure which process uses more. In theory I can recycle both bottles, but I think that only glass recycling is effective around here. (Not sure how many classes of things are being collected to get people used to it, but the downstream technology isn't there yet). But glass recycling was always more about keeping landfills tidy than saving resources, as IIRC the energy differences are negligible between recycling glass and new glass, and it's not like we're running out of sand in the world.
* You may substitute tomato ketchup in the bottle in your mind if you prefer. But I am not you, so prefer not to.