Eu quero comprar outro livro.

Yes, you can often leave it out.

Portuguese is a pro-drop language, which means the subject pronoun is often omitted when the verb ending already makes the subject clear.

• Eu quero comprar outro livro.
• Quero comprar outro livro.

Both are natural in Brazilian Portuguese.

You might keep eu when:

• you want emphasis
• you are contrasting with someone else
• you want to be especially clear

Example:

• Eu quero comprar outro livro, mas ele quer comprar uma revista.

Because quero is the conjugated form of the verb querer for eu in the present tense.

The verb querer means to want. Its present forms include:

• eu quero
• você quer
• ele/ela quer
• nós queremos
• vocês querem
• eles/elas querem

So eu quero means I want.

Because after quero, Portuguese uses another verb in the infinitive to express what someone wants to do.

So the structure is:

• quero + infinitive

Examples:

• Eu quero comprar outro livro.
• Eu quero estudar português.
• Eu quero viajar amanhã.

This is very similar to English want to buy, want to study, want to travel, except Portuguese does not use a separate word like to between the two verbs here.

In Portuguese, outro often appears without an article when it means another.

So the most natural basic form is:

• outro livro = another book

Using um outro livro is possible, but it can sound:

• a bit more emphatic
• a bit more specific in some contexts
• less basic than the simple form

For most learners, the safest default is:

• quero comprar outro livro

not

• quero comprar um outro livro unless you have a reason for the extra nuance

Because livro is a masculine singular noun, and outro must agree with it.

Agreement:

• outro livro = another book
• outra revista = another magazine
• outros livros = other books
• outras revistas = other magazines

So outro changes form depending on the gender and number of the noun.

Here, outro means another.

With singular nouns, outro/outro(a) often means:

• a different one
• an additional one, depending on context

So outro livro can mean:

• another book
• a different book

The exact nuance depends on the situation.

For example:

• If I already bought one and want one more, outro livro can mean another book.
• If I do not want this book but a different one, it can mean a different book.

They often overlap, but there is a slight difference.

• outro livro = another book / a different book
• mais um livro = one more book / an additional book

So:

• Quero comprar outro livro can suggest another or a different book.
• Quero comprar mais um livro more clearly suggests one more book.

If you specifically want to emphasize quantity, mais um is often clearer.

This is the normal and most natural word order:

• Eu = subject
• quero = conjugated verb
• comprar = infinitive
• outro livro = object

So:

• Eu quero comprar outro livro.

This is the standard pattern in Portuguese for this kind of sentence.

Other word orders are possible in special contexts, but this is the one learners should use.

Yes.

• Eu quero comprar outro livro = I want to buy another book
• Eu quero outro livro = I want another book

The second version leaves out comprar because the action is understood from context.

So if you are in a bookstore, Eu quero outro livro may be perfectly natural.

Eu quero... is grammatically correct and common, but in some situations it can sound a bit direct, especially when making a request.

A softer option is:

• Eu queria comprar outro livro.

Literally this uses the imperfect, but in practice it often works like:

• I’d like to buy another book

You could also say:

• Gostaria de comprar outro livro.

This sounds more formal or polite.

So:

• Eu quero comprar outro livro. = direct, neutral, natural
• Eu queria comprar outro livro. = softer
• Gostaria de comprar outro livro. = more polite/formal

A simple approximate pronunciation is:

• eh-ooh KEH-roh kom-PRAH oo-TROH LEE-vroh

A few helpful notes:

• qu in quero sounds like a hard k
• rr is not used here; the r in quero is a single r
• outro is commonly pronounced something like ô-tro or ow-tro, depending on accent
• livro can be tricky because of the vr cluster

A rough syllable breakdown:

• Eu
• que-ro
• com-prar
• ou-tro
• li-vro

Because outro is one of the words that normally comes before the noun in Portuguese.

So:

• outro livro
• outra casa
• outros amigos

This is different from many descriptive adjectives, which often come after the noun:

• livro interessante
• casa grande

So learners should remember outro as a pre-noun word in normal usage.

In outro livro, outro is functioning as a word that modifies the noun livro, so learners usually think of it as an adjective-like determiner.

If the noun is omitted, it can also stand alone:

• Quero outro. = I want another one.

So in practice, outro can behave:

• like a modifier before a noun
• like a pronoun when the noun is left out

For a beginner, the main thing to remember is:

• before a noun: outro livro
• by itself: outro = another one