The last few years have seen a boom in the publication of teen fiction in Indonesia. Particularly since the publication of the highly successful novel Eiffel ... I’m in love (Arunita 2001), numerous fiction works targeted at a youthful readership have appeared. This genre of popular literature has been so successful in attracting its audience that it currently constitutes the largest growing market in the Indonesian publishing industry (Simamora 2005). One of its striking characteristics is the predominant use of colloquial Indonesian, an informal variety of Indonesian that is closely identified with speakers from the capital Jakarta, particularly young people. Over a decade ago, scholars noted the increasing use of colloquial Indonesian in popular literature (see for example Adelaar and Prentice 1996:678). The implication is that this language variety has spread into domains previously dominated by standard Indonesian, the formal variety used in government administration, formal education, and most printed mass media. Indeed, contemporary Indonesian written literature is largely associated with standard Indonesian, such that the increasing use of colloquial Indonesian in popular literature has invited much criticism from language gatekeepers. Despite such criticism, however, teen fiction continues to flourish. The increasing use of colloquial Indonesian in teen fiction, though noted by scholars, has not been subject to any detailed linguistic study. Linguistic studies of colloquial Indonesian – at least those published in English – have focused so far on its use in speech, or in written texts intended to resemble speech, such as internet chatting and advice columns for young people. Prior to the recent surge in teen fiction, use of colloquial Indonesian in contemporary written literature was largely limited to dialogues. Writers such as Putu Wijaya, for example, are known to incorporate colloquialism to render dialogues more natural (Rafferty 1990:107). Teen fiction writers have extended the use of colloquialism into other parts of fiction such as the description of characters, settings, and inner thoughts. This development makes it interesting to look for a way to describe the increase of colloquialism. A useful approach is to examine the usage patterns of a term or a selection of terms in a number of teen fiction works published over time, with the purpose of observing changes in the patterns, and whether such changes can be shown to represent greater colloquialism. This study is a preliminary attempt in that direction. My purpose here is to demonstrate that in the last two decades during which colloquial Indonesian has been employed in teen fiction, there has been a shift in writing style from one that bears greater resemblance to standard Indonesian towards a style that is more colloquial. The term ‘style’ is commonly employed in sociolinguistics to refer to ways of speaking, which Bell (2001:139) defines in terms of the question ‘Why did the speaker say it this way on this occasion?’ (italics in original). Adapting this definition for teen fiction writing, I use ‘writing style’ here to refer to the characteristic manner in which an author writes fiction. This style is observed here by examining the use of the preposition pada ‘to, towards, on, in, at’ as compared to the use of three other prepositions, namely kepada ‘to, towards’, ke ‘to, towards’, and sama ‘to, towards, by, with’. The development towards increased colloquialism is shown through two indicators: a reduction in the range of prepositional meanings of pada along with the assignment of particular discourse functions to kepada, and an increased use of ke and sama. The data are drawn from ten works of fiction published between 1998 and 2005. Eight of these are written by the same author, Hilman. In four of them, Hilman collaborates with fellow writer Boim Lebon. The other two works are by Laire Siwi Mentari and Marthino Andries. This selection is motivated by the following considerations. Hilman’s works have been highly and consistently popular since his first publication appeared in 1986. They span two decades and therefore provide an appropriate time span for examining shifts in writing style. Laire Siwi Mentari and Marthino Andries are also successful writers; their first novels were published in 2004, followed by their second novels in 2005. This study makes use of their second novels.