It was explained to me that "Lo siento" would be used to express sympathy or condolence: "I'm sorry that happened to you." ("I feel bad.") "Disculpe" would be used to apologize for something for which one was taking responsibility: "I'm sorry I killed your plant." ("It's my fault.") "Perdon" would be used to excuse oneself: "I'm sorry for interrupting." ("Pardon me.")

It is a little complicated because in some cases you may use one or another but I general I would say: "Disculpa" is often used to call for someones attention whom you usually don't know, for example: "Disculpa, ¿podrías decirme que hora es?" is like saying: excuse me could you tell me what time is it? ASKING FOR SOMEONE'S FORGIVENESS OR APOLOGIES: in order of formality: Perdón, Disculpa y lo siento PERDÓN: You can use it as a verb: "Perdóname, no quise herir tus sentimientos" means: "I'm sorry I didn't mean to hurt your feelings " or as a noun: "Quisiera pedirte perdón por haber causado tanto daño" means: "I'd like to ask for your forgiveness for causing so much damage" DISCULPA: as a noun. "pedir disculpas" is like "ask for an apology" which is less formal than asking for someone's forgiveness (asking for "Perdón") DISCULPA/LO SIENTO: as a verb, you can use it in daily insignificant incidents such as hitting someone's shoulder when you're walking or maybe if somebody gives you your change wrong you ussually say: "Lo siento" or "Oh! disculpame" Finally you can use "Lo siento" to express somebody your feelings about what has happened (ussually a bad thing) to that person for example if you know that a girl/boyfriend of a friend of you had left him/her you say: "lo siento" Hope I was clear enough =) Regards!

Interesting question. Lo siento - it is like a very formal way to say sorry. Lo siento literally means -I feel it- When it is used in spanish? well it is used the same as Perdón for everytime you make a mistake but not a big deal or to serious, like when you push someone you can either say Perdón or Lo siento.It is also used a lot when you feel bad for someone else. If something bad happened to someone you know you say -lo siento-. Perdón- This word is very easy cause it is the same as in english, forgive me - perdoname. Sorry for being late-Perdón por llegar tarde. unforgiven-imperdonable. This word can be used when something really bad has been done. Disculpa- This one is similar to -excuse me- For example. ¿Disculpa me das la hora?-Excuse me could you tell me what time it is? This word can also be used as sorry. Examples. Perdón por llegar tarde-Sorry for being late Disculpame por llegar tarde-Sorry for being late Siento llegar tarde-Sorry for being late. In most cases these words could be used and they mean the same.

Since you have good answers , my contribution for you is this little scene from "Spanglish" (2004): https://www.youtube.com/watch?v=0C6Ja2upiKA