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If one owns 75% of company shares, does that mean that he would have to take upon himself 75% of the company's expenses?
You can look at the company separately from the ownership. The company needs money that it doesn't have, therefore it needs to borrow money from somewhere or go bankrupt.  And if they can't get money from their bank, then they can of course ask people related to the company, like the two shareholders, for a loan. It's a loan, like every other loan, that needs to be repaid. How big the loan is doesn't depend on the ownership, but on how much money each one is willing and capable of giving. The loan doesn't give them any rights in the company, except the right to get their money back with interest in the future.  Alternatively, such a company might have 200 shares, and might have given 75 to one owner and 25 to the other owner, keeping 100 shares back. In that case, the shareholders can decide to sell some of these 100 shares. I might buy 10 shares for $1,000 each, so the company has now $10,000 cash, and I have some ownership of the company (about 9.09%, and the 75% and 25% shares have gone down, because now they own 75 out of 110 or 25 out of 110 shares). I won't get the $10,000 back, ever; it's not a loan but the purchase of part of the company.