Looking on the internet deeply has found these results:

Who I was travelling with is the most popular phrase on the web.

whom I was travelling with 173,200 results on the web	Who I was travelling with 190,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I was travelling in old Egypt and I befriended an ancient wise man. Commissioner, yesterday I was reading a British paper whilst I was travelling to Strasbourg. I learnt to cook when I was travelling around with the army. Don't judge me because I was travelling with those sheep. I met the prince when I was travelling with your grandfather. I was travelling there to seek work when the maenads abducted me. I bought this when I was travelling. I was travelling with my family once.	I was travelling there to seek work when the maenads abducted me. Marty O'Connor was travelling with his business manager, Kate McVie. But I was travelling in third. I met the prince when I was travelling with your grandfather. Don't judge me because I was travelling with those sheep. I was travelling with my family once. I learnt to cook when I was travelling around with the army. Commissioner, yesterday I was reading a British paper whilst I was travelling to Strasbourg.

whom I was travelling with

173,200 results on the web

Who I was travelling with

190,000 results on the web

More popular!

I was travelling in old Egypt and I befriended an ancient wise man.
Commissioner, yesterday I was reading a British paper whilst I was travelling to Strasbourg.
I learnt to cook when I was travelling around with the army.
Don't judge me because I was travelling with those sheep.
I met the prince when I was travelling with your grandfather.
I was travelling there to seek work when the maenads abducted me.
I bought this when I was travelling.
I was travelling with my family once.

I was travelling there to seek work when the maenads abducted me.
Marty O'Connor was travelling with his business manager, Kate McVie.
But I was travelling in third.
I met the prince when I was travelling with your grandfather.
Don't judge me because I was travelling with those sheep.
I was travelling with my family once.
I learnt to cook when I was travelling around with the army.
Commissioner, yesterday I was reading a British paper whilst I was travelling to Strasbourg.